An irregular period can feel like your own personal surprise party — especially when you’re planning to go anywhere near a bathing suit. But while most irregularities in your cycle are not cause for concern, there are a few factors to pay attention to if you notice the pattern of missed periods becoming a little too familiar.

But first things first: what actually constitutes an “irregular” period? According to Ob/Gyn Marcelle Pick, that depends a lot on you.

“A textbook period happens every 24-29 days, but in truth what is ‘regular’ covers a wide range,” she writes on her site Women to Women. “Cycles between 23 and 35 days are very common. A woman may get her period only one to four times a year. Or she might have periods that occur two to three times in a month and involve spotting or extremely heavy flow. Alternatively, she may have heavy episodes of bleeding every two to three months. Irregular periods are simply what is irregular for you.”

In other words, normal covers quite a broad spectrum. That said, random spotting or long periods with a heavy flow are never fun, and your doctor can prescribe options like hormonal birth control pills to help regulate your flow. You know your body best, so talk to your gyno if you notice something’s up.

But let’s say a missing period is your problem. We’re just going to get this out of the way: take an at-home pregnancy test. Those sore boobs you’re silently cursing? If you’re sexually active, that might not just be PMS. Your doctor will want to rule this out first, so it’s best to be sure.

If you’re certain your wonky cycle and overwhelming craving for tacos is not baby-related, though, here are some of the most common reasons your period could be off (and how to deal).

1. You’re stressed out

Okay, we’re all frazzled in one way or another. But whether it’s a looming deadline at work or troubles in your love life that are causing you anxiety, your body still produces the fight-or-flight hormone, cortisol, in response — and churning out cortisol takes precedent over the sex hormones like estrogen and progesterone that regulate your period, according to Dr. Pick.

“I describe it to women as whatever stress you’re under, your body decided it was not a good time to get pregnant. It’s your body’s way of protecting you,” Ob/Gyn Melissa Goist told Cosmo.

So if you’ve missed one month due to a particularly crazy few weeks, it’s not something to freak out about so long as you are able to relax going forward. But if chronic stress is causing a prolonged disruption, you should talk to your doctor about treatment options and ways to cope.

2. You’re hitting the gym too hard

Cortisol can be one tricky bastard. Whether you’re training for a marathon or simply overdoing it at spin class too often, your body treats overtraining as stress, explains nutrition expert Dr. Josh Axe. Cortisol provides your body with glucose for a rush of energy to address dangerous or stressful situations, but can wreak havoc when it’s supplied in a constant stream — havoc like causing amenorrhea, or the absence of one or more menstrual periods.

According to a report out of the University of Michigan, running, ballet, and bodybuilding are the most common forms of exercise that cause amenorrhea, but certainly not the only ones. If you think this could be the case for you, try cutting back on the length and intensity of your workouts.

Cortisol is not the only issue at play here, though: missing your period can also correspond with your overall body fat. When your body mass index (BMI) falls below 18.5, studies show it can throw your cycle off — and that’s when it’s time to hit up to a doctor or nutritionist.

“Body fat is important for creating enough estrogen, which is why very thin women or those with serious conditions like anorexia and bulimia can experience absent or missed periods,” Dr. Axe notes on his website. “Increased physical activity and nutritional demands of intensive exercise can sometimes lead to a low body weight that put you at risk for hormonal problems.”

3. Your drinking habits are to blame

Drinking caffeine (over 300 mg a day, or more than a Starbucks Venti coffee) can shorten your period and your overall menstrual cycle, studies indicate. That doesn’t mean you need to go cold turkey (in fact, coffee has numerous health benefits), but you may want to cut down if you’re hitting the cold brew four times a day.

Similarly, ingesting booze (even socially) can disrupt your reproductive system, according to medical studies. Alcohol can temporarily boost your level of testosterone, which is known to suppress the hypothalamic–pituitary unit, or the part of your brain and endocrine system that work together to control the secretion of reproductive hormones and trigger ovulation. The result? Your period could go missing for a month (or M.I.A. altogether).

The risks are higher the more caffeine or alcohol you drink, but the amount it takes to throw off your cycle varies from woman to woman. So it’s best to talk to your doctor if you feel you fall into either camp.

4. You could have PCOS

Polycystic ovary syndrome (PCOS) affects as many as 10% of women of childbearing age. PCOS is an endocrine disorder that causes your ovaries to produce too much testosterone, which, as we mentioned, can stop ovulation. The causes are unknown, and it can spontaneously develop even if you’ve never had symptoms before.

Signs to watch for are infrequent or abnormally prolonged periods, excess hair growth, acne, and weight gain, reports the Mayo Clinic. It’s best to hit up your Ob/Gyn if you notice any or all of these symptoms. Your doctor can usually detect PCOS with a simple ultrasound test by identifying the fluid-filled follicles along the ovary wall that are the condition’s calling card.

Even more reason to get checked out if you think this could be the culprit? PCOS is also associated with an increased risk of type 2 diabetes and heart disease, but these complications can be greatly reduced by treatment (often with birth control pills) and early detection.

5. You’ve got thyroid issues

If you’ve noticed a theme here at all, it’s hormones. So, let us introduce you to one more: thyroid hormone, or TH, which regulates functions like metabolism, heat production, and blood pressure. It’s secreted by the tiny, butterfly-shaped thyroid gland in your neck, and also interacts with the female reproduction system to stimulate ovulation, according to Johns Hopkins. When your thyroid acts up, it can cause heavy periods or stop it entirely — and women are five to eight times more likely to have thyroid dysfunction than men.

The disorders fall into two camps. First, there’s hypothyroidism, when too little TH is released. Symptoms include fatigue, depression, weight gain, and a whole host of other issues that are easy to mistake for run-of-the-mill ailments. Hyperthyroidism occurs when too much TH is secreted, causing issues like nervousness, weight loss, lack of appetite, and insomnia. One symptom of both? Irregular periods, whether heavy (hypo), or scant (hyper).

The good news is that treatment is available, and thyroid disorders can be detected with a simple blood test. Your doctor will most likely automatically recommend this if you’re experiencing an irregular cycle or other symptoms associated with thyroid disorders, so making an appointment to double check can’t hurt.

At the end of the day, our our menstrual cycles are pretty damn complicated. But armed with the right information, you can ensure that it’s smooth sailing (or flowing) from here on out.

Eva Medoff is a writer and editor in Brooklyn, NY. She enjoys making her own candles, cooking vegetarian meals, and adding to her overalls collection (five pairs and counting). You can follow her attempts to become the indie Martha Stewart (read: broke DIY queen) on Instagram @cityandfox, and check out more of her work on her website.