Thank you for your question! During the first 1-2 years after a young woman starts her period, her cycles may be irregular; however, after that the menstrual cycle will typically vary between 22-35 days. Irregular cycles may be the result of stress, intense exercise, weight loss, diet or a hormone imbalance. However, if you are having unprotected sexual intercourse or close sexual contact, it could also mean that you are pregnant. If you think you may be pregnant, it is very important to see your health care provider. If you skip many periods, you should talk to your healthcare provider and see why this is happening.