While I've never really had much of an acne problem, I can completely understand how you feel here. I got bullied a lot in school, so I never had much confidence in myself either, especially in my physical appearance. I suppose the only difference between you and I in this case is that the root of my problems were in that I believed the bullies over just about anybody else while in your case, you're really not content with how you look because of your acne. Still, I don't think we're that different.
Yume's advice about trying some different treatment for your skin might help. I'm sure there's something out there that will work, but nothing changes overnight. Just be persistant and once you're satisfied with yourself, what other people think won't matter as much to you. That or you could just accept yourself the way you are and ignore the people who are slowly killing off your self-esteem. Which...is very hard to do.