What Causes Heavy And Painful Periods?

i am having serious cramping. i got my period yesterday and it is never this heavy. i can't sleep because of the pain from my belly button down. my back is sore as well. i've been on the pill for about 8-9 months, i am sexually active. my period is usually lighter but it is extremely heavy right now and i haven't had pain like this since i first got my period. what is wrong?