Bleeding again after AF?

This is our fifth month trying to conceive #2.  My last AF started 3/9 and lasted until 3/16 but there was still a little brownish discharge on 3/17.  This AF lasted longer than it usually does but it wasn't any heavier than usual.  I started using OPKs and i had two days of blank circle and this morning I got a blinking smiley.  I was so excited but then this afternoon I started bleeding again.  Not heavy, but there when I wipe and a bit on a pad.  Does anyone know what could be causing this?  Has this happened to anyone? I feel like it's the AF that just doesn't end!!