That doesn't sound like someone you should be with, at least not at the moment. It definitely sounds like he just wants some time to himself, though he should probably just come out and tell you that instead of trying to get you to figure it out. Maybe next time you talk to him and he seems to be in a bad mood, ask him if he wants to talk about it or if he just wants to be alone for a little.

I was in a mood like this the other night (not exactly the same, but somewhat), I had a terrible day and didn't really feel like talking to anyone. My girlfriend texted me while I was at work, so I texted her back when I got home that night and told her I was in a really bad mood from work and just wanted to lay there doing absolutely nothing for a while. She wanted me to feel better, and I told her the only way I would feel better is if I just had some time to myself. That's not exactly something that a boyfriend/girlfriend likes to hear from the other, but it was true at the time. After I just laid in bed staring at the ceiling for a while I called her and apologized for it, but I just really needed some time alone.

That sounds basically like what's going on with you, only to a much higher degree. If he seems to just want some room or some time to himself, then let him have it. But if this keeps going on for a while longer, then he probably isn't right for you, I know I would hate it if everytime I wanted to see my girlfriend she was too tired or busy to do anything. I could understand maybe a few times, but it seems like everytime you want to see him he's "too busy".