Why has my period been on for 15 days so far and counting?

Im 21 years old so its not menopause...ive had regular periods since i started...theyve always come on time and lasted about 5 days.....i do not take birth control or any other medication....my period came on 2 days early this month on the 9th and has been on every since...some days lighter than others but non the less...still bleeding....why?