One day period post D&C

So I had bleeding July 17th 15 days after I stopped bleeding for my D&C from June 30th. It lasted about 4 hrs and was never went on a pad. So tomorrow will be six weeks since my D&C. My OB said I should have gotten my period in a month from the D&C. I took a few pregnacy test that were faintly postive yesterday I told her about it they checked me and it said negative even the blood test said negative. But I wonder why I had postive test for a week and now nothing? Could it have been a chemical? I don't think the 17tg of July was a period she said she would consider it as a period and that I will get my period this week and if I don't just start birth control any ways next Sunday! I don't know what's going on with my body! Has anyone else had this happen to them? My OB said there shouldn't have been any HCG in my system after the D&C so why the postive test? And where is my period??