Brown spotting for 6 days.

I have a 10 month old. I had a normal period at 8 weeks pp. Then again at 4 months pp. I haven't had one since. I have been spotting brown for 6 days now. It started out a tiny amount. It has increased a little each day and it's mixing with a little red. But it's not flowing like a period. I took a pregnancy test 7 days ago and it was negative. Had this happened to anyone else??