Postpartum sex

Maddie • Mommy to a gorgeous baby girl Cora Jo
I'm about 5 weeks post partum, I stopped bleeding and my midwife gave me tho go ahead for sex and she put me on birth control (been taking it for 5 days) well me and my boyfriend had sex last night (TMI, not rough but kinda deep) and I just started bleeding a little is this the birth control or the sex??