Why doesn’t he want to have sex all the sudden?

So a few weeks ago we where having sex like multiple times a week and despite me being pregnant it was really great. I was so happy I was actually able to still do stuff and feel comfortable unlike my last pregnancy but now it’s been almost three weeks and nothing. It’s so weird because usually he’s always in the mood and I asked why he suddenly wasn’t interested even with me trying to spice it up by sending some sexy photos and he’s like I don’t just don’t want to have sex. I’m so confused and feel so gross and unattractive wondering why he suddenly doesn’t want me.

I mean it’s been almost a month of no sex. I’ve been with him for several years and this isn’t like him. Last time this happened we went five months when my daughter was born and he ended up flirting with other girls so it’s causing all this anxiety that that is going to happen again.