If you're having trouble ridding yourself of negative beliefs, try the following:

Don't fight against those negative thoughts - it only makes it worse when you say to yourself, "I know I shouldn't think it, but..." and things like that.  So instead of trying to tell your mind what to do and not do... everytime you realize a negative thought that you can't get out of your head - write it down on a piece of paper or in your journal or in an email to yourself.  This way, you can "hold on" to the negative thought, meaning since you wrote it down, you can remember it any time you want just by looking at it, but you free your mind from worrying about it any longer in doing so.  If you don't like writing just the negative thought, you can write a positive thought to counteract the negative one right after it.  For example, "I hate my complexion today, it's making me so self-conscious," then write, "I love my face, I have a beautiful smile that brightens other people's day!" or something like that, whatever you positively believe!