Now that I'm pregnant my man always wants to have sex

Now that I'm pregnant it seems like he has these unrealistic needs that I constantly feel guilty if I don't meet but the fact is I'm 17 weeks pregnant and sometimes I don't want to have sex. The bigger I get the more concerns I have, is he being to rough, have I been laying on my back for to long....the list goes on and on. I try to remind him that I'm pregnant and that his expectations of having "rounds" of sex for hours is a little unrealistic but he still makes me feel guilty about it even though he's not trying to make me feel bad, I do and it sucks. Sometimes I just wanna come home from work, eat, and go to sleep without feeling bad about it. Any advice on how to talk to him would be nice.