What Is The Treatment For Heavy Bleeding And Irregular Menstruation?

Hi, I'm seventeen I started my menstral cycle when I was 13 and continued it normally through age 15 however after that the became strangley irregular sometimes becoming absentee for 6 months I have never been sexually active .and now, my period, after being absentee for four month is extremly heavy and severe cramping which is strange because usually they are light and pain free but the amount of "blood" loss is alarming