Pullout method on 3 weeks postpartum

I am 3 weeks postpartum and bleeding still just brown blood which means old, anyways I started having sex again at 3 weeks postpartum because I didn't have any stitches after baby, we are using the pullout method cause I'm not on birth control till my 6 week postpartum check up, is it possible I could still get pregnant? I'm a nervous wreck