Your period is probably not something you look forward to. However, as you grow accustomed to the ritual, you may notice changes that occur in your body, such as a shorter or missed period. Have you been asking yourself, “Why is my menstrual cycle getting shorter?” You’re not alone. Irregular periods are very prevalent, affecting 14 percent of women of childbearing age.

An irregular period can mean a lot of things. While a typical cycle lasts around 28 days, an irregular one lasts longer than eight days. It also includes missed, early and late periods. While it’s easy to identify an irregular period, it’s more challenging to pinpoint the cause.

If your menstrual cycle is getting shorter, consider the seven potential causes below.

You Switched Birth Control

If you miss or change your birth control, your cycle length can be affected. Most pills will lessen the duration and severity of the flow. Traditional birth control options are pills packed as 21 days of hormone pills and seven days of placebo pills. During those last seven days, the menstruation cycle occurs.

More advanced options include pills that run for three months to a year before a week of placebo or low-estrogen pills. With a hormonal IUD (intrauterine device), some women miss their periods altogether. If you decide to stop taking your birth control pills, do so safely and give yourself plenty of nutrients and probiotics to support a balanced recovery.

You Were Prescribed New Medication

Beyond birth control, other types of medications — both over-the-counter and prescribed — can affect your menstrual cycle. If you take aspirin regularly to prevent blood clots, it can make your flow heavier and longer than usual.

Certain antidepressants have been found to cause heavy bleeding, painful cramps and missed periods. Experts say you’re most likely to notice the side effects in the first three months after you start the medication. Other drugs that can affect your period include warfarin, thyroid medication, epilepsy treatment and chemotherapy.

You Just Went Through Puberty

Your hormones can go haywire after going through puberty. Two hormones that have an impact on the menstrual cycle include estrogen and progesterone.

Estrogen is the hormone responsible for the development and maintenance of the reproductive system, and progesterone is a steroid involved in the menstrual cycle and pregnancy. It can take several years for hormone levels in your body to balance out after puberty, and irregular periods are common up until this time.

You’re In Perimenopause

As you age, your body continues to change, just like during puberty. Fun, right? In some cases, the answer to “Why is my menstrual cycle getting shorter?” is the start of perimenopause. This time leading up to your last period can last a few months or extend as long as a decade.

The average woman spends three to four years in perimenopause. During this time, your body often witnesses hormonal changes, similar to going through puberty. The levels of estrogen circulating through your body can vary, affecting both the length and flow of your cycle.

You’re Breastfeeding a Newborn

When nursing, your body provides all essential nutrients to your newborn and releases the hormones that cause your body to go through menses, something called lactational amenorrhea.

Almost all mothers who breastfeed are period-free for three to six months after giving birth. Nursing mothers who do experience a period have no way of knowing whether she ovulated during that time. If you wean your child off breastfeeding, it’s likely your menstrual cycle will resume.

You Have Polycystic Ovarian Syndrome

Polycystic ovarian syndrome, often called PCOS, is a common female health problem that affects one in 10 women of childbearing age. It can cause irregular periods and complications with fertility.

If you’re concerned about changes in your menstrual cycle, look for common signs of PCOS, like fatigue and weight gain. Keep an eye out for unusual symptoms — like anxiety, depression and sleep apnea — that could point toward something more serious.

You Have a Thyroid Disorder

Changes to your menstrual cycle could be a sign of a thyroid issue. The thyroid gland, which is located in the front of the neck, interacts with various aspects of your reproductive health, including your ovaries and the sex-hormone binding globulin.

Hypothyroidism, when the thyroid gland is working below capacity, is a disorder that can cause major changes to your menstruation cycle. Those with the illness may see infrequent or absent periods, and there is a risk of decreased fertility. On the opposite side of the spectrum, some women face heavier-than-usual flows.

Why Is My Menstrual Cycle Getting Shorter?

If you’ve been asking yourself, “Why is my menstrual cycle getting shorter?” it can be difficult to determine the answer. Schedule an appointment with a gynecologist if you’re concerned about your irregular period, whether you believe it’s caused by birth control, breastfeeding, PCOS or something else.

It’s OK to be nervous before seeing a gynecologist, even if you’re an exam veteran. At the least, the experience can be uncomfortable and embarrassing. The key is to find the right doctor before you go. A seasoned gynecologist will make you feel at ease in the exam room.

If you aren’t happy with a previous experience, it’s appropriate to seek another opinion. Before your appointment, do some research on what to expect. By reading in-depth information about exams, screening tests and preventive health, you’ll face fewer surprises during your visit.