6 wks pp and pregnancy

My husband and I had sex last night and it was so good he forgot to pull out. I told him we need to get plan B now and he said not to worry about. he doubts I'd end up pregnant again right now but I got pregnant while on the nuvaring so I'm very fertile. The women in my family are very fertile. So I think if I don't take it i will end up pregnant again. So my question is, have you been in this situation where you did end up pregnant so soon after a baby? Or know anyone who has? I know it's risky Especially after a csection which I had.