What Causes Period Pains,nausea And Abdominal Cramps?

I m on birth control because I have terrible periods and have had a cyst burst 6 months ago. The birth control has been helping for a few months until recently. The period pains are back, nausea, diarrhea, cramps and heavier bleeding. I bleed quite fast through my tampons superplus and I ve been seeing a lot of clots. So I don t know if I m losing too much blood, my iron needs to be checked or change that I need to change my birth control.