Sex pregnancy am I okay??

Husband and I just had sex, for only about 3 minutes til he came (we had a lot of foreplay) anyways, he was on top, and when he finished I kind of felt short of breath I think from his weight being on my stomach. I’m almost 18 weeks and wasn’t sure if I should stop letting him be on top or if it’s safe etc? He also came inside of me I don’t know if that’s safe in general when pregnant since I was told it thins the cervix to give birth before....... Help :(