Boyfriend never in the mood

Okay so I'm super confused right now.. 
About four nights ago my boyfriend and I were talking and I wanted to start sexting because we hadn't seen each other in a few weeks due to work schedule conflicts and I was feeling horny. He flat out rejects me. If it didn't happen often, I wouldn't complain, but he has rejected me over this many times within the past few months. I can completely understand not wanting to every time, sometimes I'm too tired to or have a migraine, but 9 out of 10 times he will say no. We've been together a couple of years and I just don't know what to think. We've talked and talked about it and right when I think we've resolved something a couple weeks later it becomes a problem again. Also, when I brought it up then we tried talking about it but ended up being an argument and then it turned on me not trusting him??? I don't even know where that came from? I've never given him a reason to think I don't trust him. 
He's wonderful in every other way. Very loving and caring and he really does try his best to make me happy and I try my best to make him happy. But this issue of him never being in the mood is definitely putting stress on our relationship. I've asked him why he doesn't want to and he just says he's "not feeling it today/tonight". It makes me feel self conscious about myself, like I'm not good enough and I've told him this, but so far nothing's changed. I just don't know what to do about this. Help!!