PAIN during sex??!!??

No matter if We try doggy style, missionary, laying on our side, and I won't dare try on top because it hurts worse the deeper it is. I've tried elevating my hips with a pillow for both missionary & doggy style & that didn't do anything. We've tried with/without lube & that hasn't helped, it just kept me wet but didn't help w/ the pain. But it hurts so bad it's pretty much unbearable. With that being said it makes it that much harder to get in the "mood". My poor SO... weve only had sex like once a month since we've gotten pregnant & I'm 18weeks... is there anyone else out there that has this problem? I need help!!!