Why won't my fiancé have sex with me?HELP!!

Rachael
Him and I have been together for 8 months now. When we first started dating we would have sex all the time, he stopped wanting sex as much a couple of months ago. I know is isn't cheating because I am with him 24/7. We even work together every day. I confronted him about it and he says that it's hard to get in the mood when I'm always yelling at him. We argue about stupid things but I'm not always yelling at him.
Every time I try to start doing things he pushes me off of him and comes up with an excuse as to why we can't have sex at that time.
It makes me feel like he isn't attracted to me anymore and every time I bring it up he says that he always wants to have sex with me, but he never tries to.. Idk what to do..