Postpartum periods...

I'm 11 weeks pp(I breastfed for 1 month, now I strictly formula feed) I finally started what I think was my pp period. I only bled for maybe 3 days? I had cramps.. But it didn't feel like a "period" it was light. I usually cramp way worse to the point of me blacking out and I bleed for a week (TMI I know lol) anyways my fiancé and I have had unprotected sex many times since week 2 postpartum. I'm not on birthcontrol. Could it have been implantation bleeding? Or just a lighter period? Any help?! Thank you!