Postpartum help

I am almost 21 weeks postpartum. For the past few days, I have had blood when I clean up after going to the bathroom, but it's only once every few days. Friday and Saturday last week, I forgot to take my mini pill and pregnancy tests on sunday and monday were negative. Anyone else experience this and can help me figure out what is going on? I am nursing my daughter still. Could this be my body trying to have a period or potential pregnancy?