Uncomfortable Sex

I'm 17w4d today and (sorry if any TMI) last night my DH and I had sex. It's not sex itself that bothered me, but with him on top in a missionary position the pressure on my stomach made it hard for me to breath. I told him and of course we switched things up. I'm not a skinny girl and I am starting to show but I didn't think slight pressure would make me short of breath. Anyone else have similar issues?