Implantation bleeding?

I gave birth a little over 7 weeks ago and my fiancé and I had sex for the first time about a week ago. I hadn’t started my birth control because my one month appointment was after my first “period” after having my son and I wasn’t supposed to start until the day of my next period which hasn’t happened yet and isn’t scheduled for another 9 days.

But my stomach has been in knots for the past 3 days and I’m now bleeding brown which indicates old blood.

Is this implantation bleeding or just my body still getting rid of gunk from giving birth?

Edit: he did pull out but of course we weren’t as careful as I would have liked to be this soon.