It could be what I have, a left over blood clot in your uterus. My first AF was fine, but with my second AF was finished, I started bleeding again 3 days later. Then I continued to stop and start for another week before I went to the doctors. I got an u/s done and discovered a large blood clot was in my uterus.
I'd go see your GP if I were you, see if they can get you into for an u/s.