Just wondering if anyone else has experienced this?

I am 18 weeks pregnant, and i am finally starting to show! my lower stomach is getting "fuller" and feels pretyt tight most of the time. Up until now has been no problem and i definitely have had an increase in desire for . Although, the last few times my fiance and i had , its is very uncomfortable for himt o be on top of me, it almost feels like its hard to breathe and theres a lot of pressure. I tol dhim we should stop having in that position, for my comfort. Of course he understands and is not bothered by it. Just wondering if this is normal?