Implantation bleeding?

So the hubby and I have not been using protection or any withdrawal method the past couple of times. This evening I noticed some brown blood when I wiped. Hubby thinks it's just because we were a little rough last night. Idk what I think.

And some other background info: I just ended my period about a week ago, and I am three months postpartum. Yes I know you are super fertile after a baby.