I'm 16, and i've been menstruating for 5 years. just recently (4 months), i've been having my period every 17-19 days. whats wrong?!

Irergular periods : Irregular periods are one of the most common problems obgyns treat. If this is one time problem it usually resolves on its own. If this is a recurring problem you should be evaluated. There are many options available to help regulate the menstrual cycle. Schedule a visit.

Irregular periods: By 2 years after first period, most women have regular cycles. Irregular or overly-frequent periods can have many causes - from benign (e.g. Stress) to medical (e.g. Hormonal irregularities, etc.). Only a doctor can help you sort out which is causing your difficulties. Particularly if the frequent bleeding is causing you to be anemic, oral contraceptives might help with period regulation.