What Causes Heavy Bleeding And Stomach Cramps During Periods?

hi, im 20 years old, i am sexually active and have been taking femodette 2 months as i changed pill. I come off my period last week and have been taking the pill again since 8 days ago, however i have noticed light bleeding for the last 5 days, and now it is very heavy and the worst period i have ever had. I have quite bad stomach cramps too, but i am not even half way through my pack of pills and only recently had a period. What shall i do? and how long will this last?