Hi, Menstrual periods are often irregular during the first few years after menstruation starts. It may take several years for the hormones that control menstruation to reach a balance. Causes of missed or irregular periods include: Pregnancy. Excessive weight loss or gain. Although low body weight is a common cause of missed or irregular periods, obesity also can cause menstrual problems. Eating disorders. Increased exercise. Missed periods are common in endurance athletes. Emotional stress. Illness. Travel. Medicines such as birth control measures which may cause lighter, less frequent, more frequent, or skipped periods or no periods at all. Hormone problems. This may cause a change in the levels of the hormones that the body needs to support menstruation. Illegal drug use. Problems with the pelvic organs  such as imperforate hymen, pcos, asherman's syndrome... Consult Gynecologist....