It may not really be AF yet. The same thing happened to me and it went away.

My Lochia stopped at 3 weeks and then somewhere between 4-5 weeks I started bleeeding again. I was told it was AF but it was pretty light and very little cramping. It only lasted a few days. Then sure enough 3 weeks later the same thing happened. I was so bummed as I too am BF and did not want AF back yet. That was almost 3 months ago though and I have not seen her since. I think my body was just adjusting to all the hormone changes.