I had the same issue during my second trimester, but thankfully no longer have that issue. Now I'm just too big to bother attempting to have sex! lol My issue was a hormonal thing, and we did try some different lubricants, which didn't seem to help much. My husband and I just ended up spending more time on foreplay, and brought a toy into the mix. That helped me a lot, and him also, as he gets more excited when I am enjoying myself than when it seems to him like I'm just taking care of a chore.
Good luck, and I hope things resolve for you soon!