I would suggest calling the MD my sister had a similar situation where she was on her period for almost 40 days, it would go away 1 or 2 days and then come back, the loss of blood can make u very weak and for her it turned out to be low hemoglobin levels, they are suppoed to be at 13 or so normal and hers were not even 4 so she had to have a blood transfusion to help her levels boost. I would strongly recomend making an appointment specially if your getting heavy bleeding!! Good luck!
Have you missed any pills? If you miss pills it can cause you to be very irregular. If your taking your pills correctly, then I suggest calling your dr and talking with him/her.