Sex Drive Depleted (TMI- mature mommies only)

I am 31 weeks + 2 days and I am totally not excited the least little bit about sex with my SO. I am attracted to him still in every way but when it's comes to that I am just not on the band wagon . I feel bad because I know he wants it but he doesn't say anything or make me feel bad about . I'm just big at this stage and a lot of positions are just plain uncomfortable for me. Not to mention that I have begun to get nauseous right after sex itself which furthermore makes me not look forward to it. I'm sure other mommies have dealt with this but what about the nausea after and how did you find a common ground for you and your partner. I don't want to make him go without for the next 2 months especially when he will have to go 6 weeks postpartum without. I just feel like a bad partner. HELP!!!!