What Causes Irregular Periods With Prolonged Bleeding?

good evening doctor...i m neema sharma,18 yrs old from bhilai,chhattisgarh,india.Since when i was 12 yrs my menses started and they were never regular.Everytime periods continue for minimum 15 days and manytimes even more.Sometimes they continued for even whole month...even now my periods started on 6 december and it is bleeding very very heavily....please help me and suggest medicines for me...i m in great mental and physical trouble...