[ASDFJKL]

I've pretty much been together with this guy for four months. Things are getting pretty serious and I care about him a lot. He says he feels the same way, but the other day when we were fighting he told me he simply can't trust me. He says he pretty much doesn't believe most of the things I say. I think I know why he feels this way. First of all, I am not the most open person in the world with him; I wish I knew why. When we talk, it's mostly him talking and me asking questions. When it comes down to me talking, I actually feel UNCOMFORTABLE...which is bizarre, because I shouldn't. I feel like he just doesn't care about my problems as much as he says he does. Second, he also says I hide things about myself, my past, and my guy friends (who he had some jealously issues with)...does he really want me to spill all? I feel like I only need to tell him the stuff that matters. Why bother telling him something unimportant if it's just going to hurt him? Third, I think he thinks I lie about a lot of things, which I don't. I have bad luck. Most of the time it's because of a misunderstanding...or if it's something in the past I might have forgotten all the details so it sounds like I'm lying. So basically we've got a relationship that is all about him. I know a lot about him because he shares things...he doesn't know much about me because I don't. I feel this ties in with trust. So...

1) Why exactly am I so uncomfortable with talking to him about my problems?
2) What can I do to earn his trust, which is obviously the most important thing in a relationship? How can I fix things?

Thanks...sorry this post is a little confusing. But I am confused...