pregnant again?

I had my son almost 10 weeks ago. I stopped bleeding at 4 weeks postpartum and had sex for the first time at 6 weeks postpartum. My partner and I did use a condom but he did put it in without one for a few minutes first. I haven't had a period yet since I'm breastfeeding but today I wiped and noticed some brownish blood. Could that be implantation bleeding or am I getting my period? Would I have gotten pregnant from pre cum? I want to take a pregnancy test tomorrow but idk if it's too early. Any advice? Thanks!