Two months back I used birth control pills to help me get my periods back as I was put on depo injection and hadn't got my periods for over five months.I stopped the bith control pill last month just before I got my periods and they we're normal.now when I was supposed to get my periods I got brown spotting more like discharge and three days later it changed to be pinkish blood not so heavy lik a normal period,it has went on evry morning for nine days nw.I took a prenancy test four days ago and it was negetive and I also startd having headaches and upset stumuch.what could be the problem?