I need advice!(NO Pics) vaginal pain during sex?

FTM, first pregnancy, 21 y/o. So this has happened twice now in my pregnancy. I didn't think much about it the first time because I figured it was just a fluke. So basically my husband and I were beginning to have sex, I was plenty turned on but my vagina was not having it. It seemed that it was basically trying to close off or was too swollen for sex? It was absolutely, completely uncomfortable. I know more blood flow during pregnancy causes swelling but I never thought it would cause pain during sex? I'm 24 weeks tomorrow. I have obviously been attending my monthly OB appointments and everything is normal. (Yes I plan to ask my OB about this at my next appointment)
So in conclusion, I've had plenty of enjoyable sex with my husband throughout the pregnancy except for these two instances. I normally wouldn't post but I just really want to hear if any of you ladies had similar experiences? I'm not in any pain afterwards because we obviously stopped but I'm just a little frustrated & weirded out honestly. Thank you in advance, any advice/comments are appreciated!!