Lack of Sex

I've spent time googling and searching on this topic and didn't find much help, so I thought I'd try here.

I've been with my husband for 3 years now and we've always had a pretty great sex life. There have been lulls, but we typically don't go longer than a week without. It's usually worse in the winter months.

The last month or so it's been different. The last few times we've tried to have sex, he's gone soft. He's super embarrassed about it. I've asked if it's because I'm pregnant (almost 25 weeks) and it's getting real that there's a baby inside me, but he says it's not that and he doesn't know what it is. He says it's just the typical winter lack of libido and he needs to lose some weight. He's super loving and we cuddle, just no sex. We managed to have sex once last week after lots of foreplay, but he was in a rush to finish to make sure he could last.

I feel like he's psyching himself out of even attempting sex. Other than waiting and being supportive, I don't know what else to do.

My trying to initiate just makes him feel more pressured and I know if I bring up going to the doctor will be met with more feeling of inadequacy.

I'm just at a loss.

I love him and his affection, but I miss sex.

I'm almost 31, he just turned 34.