Sleep Sex..Help.!

I'm 4 weeks postpartum. The other night my husband and I had sleep sex..just like it sounds, sex in our sleep. It normally happens when we go a bit of time without doing the deed. And, it isn't normally a problem, because I am normally on BC, or trying/pregnant. The problem is, we weren't supposed to have sex yet, and I can't go on BC yet, since I'm not far enough postpartum.

I checked..and my cervix is low and open. What are the chances that I get pregnant again so soon.? I'm kind of freaking out..this is our 3rd child, I am not ready for #4 yet.

Yes, we were both asleep.

And, I am breastfeeding, and pumping extra.