Prolonged bleeding

I'm almost 9 months post partum, and I just started my 4th period. I bled like normal for 4 days and thought it was done. Had sex the next day, and started bleeding again. In total, I've been lightly bleeding for going on 13 days now. For the past few days, I see bright blood when I wipe but it's dark almost black on my pad. Is this normal? How long is too long to be bleeding/spotting like this?