What Causes Heavy Bleeding And Dizziness During Menstruation?

I haven''t had a period since august all tests came back negative. The doctor put me on birth control and i am on my third day of my period now. The bleeding is atrocious I am going through a pad an hour I am clotting and i am dizzy and weak. The cramping is horrible I have tried mobic, ibuprofen and tylenol 3. What should i do?