Hello. I totally see what you mean, and there is (it's only my point) only one solution for your problem. It's practicing. Watch american films in VO(ST), chat on IRC (#planeshift@Freenode

), read books in english, eat english, drink english, wee english..

I'm natively french-speaker and I've learned english since I was 8. (I've stopped my studies at 20). Now I'm 25 and I know I still have a lot of work to speak (at least write) english fluently. I can feel it gets better but it's work like I've written up there.
Don't discourage you and make it work.