I'm not sure where to start, but I'm a guy, and I'm having some issues, that I think are because of some stuff from my childhood. I'm not really sure, but I'm finding it really hard to be sexual with my girlfriend. Besides just not really having ever done that much before, it brings up a lot of thoughts and feelings that really mess with my head, then I just can't. Anyone else here ever have a problem like this?
Please go see either a psychologist or a psychiatrist. This stuff won't go away overnight, and as you yourself said, you're finding it really hard to be sexual with your girlfriend.
I agree with Aussie; it is important that you seek professional help now. If not, it will haunt (strong word, but true) for the rest of the days of your life. Thinking you can deal with it on your own, chances are you will not be able to do so.
And to add, don't be embarrassed. You are not the only one (male) that has had things from their past affect their life--in all areas of there life. Again, can not stress enough, the need to seek professional help.