The length of your periods may also vary - sometimes your period may last 2 days, sometimes 10. That's because the level of hormones your body manufactures can be different from one cycle to the next and this affects the amount and length of bleeding. If you're not regular, you'll want to pay attention to the clues your body may give you. At some point as you grow, your cycle will probably settle into a recognizable pattern. Disorders of the thyroid gland can cause menstrual irregularities if the levels of thyroid hormone in the blood become too low or too high.
Some women have irregular periods because their bodies produce too much androgen.
High amounts of androgen can also cause hair growth on the face, chin, chest, and abdomen, and is sometimes associated with excessive weight gain. If a teen has one of these problems, or if her periods are irregular for other reasons, the doctor may prescribe hormone pills or other medications hat will help her to have regular periods. In the meantime, if your periods are irregular, try keeping some pads or tampons in your backpack, just in case. It's important to see a doctor if you're sexually active and have missed a period - this could be a sign that you're pregnant. You should also see your doctor if you start having periods that last longer than 7 to 10 days or are accompanied by severe cramping or abdominal pain.