This stupid site on my phone, I just typed this long response and it deletes it... I'm 30x3 and having the same issue... negligee or not, the baby is still in there and it weirds him out lol.
I would talk to him. Maybe there is a reason?? Or maybe he is scared of hurting the baby? I would ask him first then plan a romantic night. Cook him dinner, wear sexy underwear. Maybe a negligee?
Yeah oral sex is the best way ;)