postpartum periods

Kaleigh
So, I breastfeed my daughter, but got my first postpartum period back when she was 6 months old. It was what I consider to be normal. The next period came just like normal and it too was a typical period for me. This month, my period was supposed to come 6 days ago. It hasn't at all. I've had period and pregnancy like symptoms. 
I took a few pregnancy tests. One came up with a faint positive that I now think is an evap line. I took a first response the morning after and it was negative. It's now a few days later and I still don't have it, but I get cramps and thick discharge off and on. 
Is this normal for a breastfeeding mama or should I still be concerned that I might be pregnant (don't know when I ovulate now after having my daughter). 
Thanks!