My period last for like 3 weeks only to stop for a couple of days then it starts again. There is some pain but I also have pcos and I am on the pill.?

Depends. You may need a different pill, would check with your doctor.
PCO, BCP, Bleeding. The amount of bleeding seems excessive to me and i recommend a visit to your doc. Pcos can cause irregular bleeding (but usually infrequent) but the bcp should correct that problem. I doubt a serious problem for you (perhaps anemia) but certainly no one wants that much bleeding. I am certain that a change in bcp or other medication can correct the problem. Best wishes.