Getting whip lash from my back and forth sex drive

My SO and I used to have sex almost every day before I got pregnant and when I started really feeling the effects of pregnancy, we slowed down. A lot. I think we went almost 6 weeks without sex. Around the middle of my second trimester my drive started coming back and I was wanting him CONSTANTLY.

But as I’m nearing my third trimester my sex drive had dropped again and he wants sex most days and I just don’t. He says he understands but he’s obviously pretty irritated by it so I try to do it even when I don’t want to and most times it hurts to the point that I have to tell him to stop before he’s done.

Does that make me a bitch for starting something I physically can’t finish? Or should he suck it up and deal? Help please.