I had a period on Feb. 11, a normal 4 day, then 2 weeks later i had a lite spotting but didnt worry (cont.)?

about it. I then had that night it hurted, then i had another period from that night til 3 days later, it went off. I waited 2 more weeks which was Friday, March 7, and had again it hurted. I had a slight discharge wit a little of blood but not much, then the next night I was bleeding and still is but it has clots and all what could have caused this?