What Causes Heavy Bleeding?

I had my period two weeks ago and ever since I have had very light spotting. Last night my period started again (day 17). Today I have been bleeding a lot heavier than usual. I have gone through a super tampon every hour and a half. I have had fibroids, polyps, and cysyts in the past and have had 2 surgeries. I also have endometriosis, but since my surgeries life has been normal. Is it all coming back again? Am I bleeding too much? I am concerned.....