Implantation bleeding or postpartum period?

So I had my second child nearly 7 months ago. My daughter has been exclusively breastfed this entire time and up until a month or so ago I was on the mini pill but stopped because it made me very moody and angry. About 2 weeks ago I had unprotected sex with my husband but he did pull out. I know the pull out method isn't a reliable way to prevent pregnancy and I know that it absolutely is possible to get pregnant while breastfeeding but I figured that between both of those things and considering I have even gotten my periods back my chances were low. About 9 days after the unprotected sex I started bleeding brown blood that only lasted two days. Is it possible that this could have been implantation bleeding? I never had implantation bleeding with my other two pregnancies so I don't know if 48 hours is too long for implantation bleeding but I know after I had my first daughter my first postpartum period lasted 18 days and was heavy as hell so the two days of light bleeding just threw me off a little.. thoughts?