9 reasons your period is late (if you’re not pregnant)

During your usual morning routine, you open your cabinet, spot a box of tampons in the back, and you suddenly realize you’re late. “When was my last period?” you think as you try to remember the last time you needed to reach for that box. Panic then takes over as your mind shoots straight to pregnancy.

While being pregnant is a possible reason for a missed period, there may be factors related to your health or lifestyle that are causing the delay, notes Shelley White-Corey, clinical assistant professor at the Texas A&M Health Science Center College of Nursing and a women’s health nurse practitioner.

Breastfeeding

Your period may not make an appearance after your baby is born, but don’t be alarmed! If you are breastfeeding your little one, a lack of periods is completely normal. Referred to as lactational amenorrhea, this is a phase that disrupts the rhythm of your menstrual cycle. After a few months, your monthly period should be right back on track.

Weight loss or weight gain

Whether you’re overweight or underweight, any change in pounds can affect your monthly cycle. Common health problems linked to weight and irregular menstruation include eating disorders, such as anorexia and bulimia, and uncontrolled diabetes. If you suspect this might be an issue for you, see your health care provider right away.

Increased exercise

Working exercise into your schedule on a daily basis is great, but excessive exercising could lead to lower levels of estrogen, which is the hormone that regulates the female reproductive process. Many athletes experience secondary amenorrhea, meaning they don’t have a period for six months or longer, from rigorous training.

Stress

A little stress in your life is fine, but chronic stress can throw your body out of balance. Stress activates the hormone cortisol and pushes your body into survival mode. If you are experiencing prolonged stress, your body can induce amenorrhea and will prevent menstruation.

Sleep schedule changes

Switching to the night shift or traveling to another time zone may prevent your menstrual cycle from starting. According to a study published in Frontiers in Endocrinology, any disruptions to your circadian rhythm—the internal clock that regulates important cellular processes—can cause you to experience irregular periods.

Medication

If you’re taking a new medication, one of its side effects may be irregular periods. A study on the effect of antipsychotics on menstruation found that amenorrhea occurred because prolactin levels were imbalanced. Additionally, some birth control medications, such as an IUD, implant or shot, may cease your periods while on them.

Thyroid dysfunction

Issues with your thyroid, such as hypothyroidism and hyperthyroidism, can disturb your menstrual cycle. The thyroid produces hormones that help regulate the body’s processes, and if thrown off balance, it can cause you to have missed periods. Luckily, there are effective treatments for thyroid disorders, so see an endocrinologist for a blood test if you think this might be an issue for you.

Polycystic Ovary Syndrome (PCOS)

Little is known about what causes this disease, but about five million women in the United States may be affected by PCOS. Like thyroid dysfunction, PCOS can cause a hormonal imbalance in your body, causing missed periods.

Perimenopause

If you’re entering perimenopause—the first stage of menopause—you may notice your periods occur more infrequently. The decrease in periods is caused by a decrease in the estrogen hormone.

If you’re experiencing irregular periods, you’re not alone. About nine to 14 percent of women in the United States are affected by menstrual irregularities. With the exception of missing your period while on some contraceptives, it is not normal to go without a period for several months and can be harmful to your health. Visit your physician if your missed periods persist.