How do I build my self-confidence?

You gotta really just look in the mirror and tell your self you're beautiful and believe it. Or... you could look up pictures of people who you know are uglier then you. Or give yourself a makeover. If you feel like your are too saggy and a F-cup like you said then just get reduction surgery turn them to a D, get better bras with better support, so instead of looking saggy they'll look big *and* perky. Get cellulite and stretch mark creams to get rid of the scars. Give yourself a makeover improve your style, how you do your hair, your makeup etc. Pretty soon you'll feel better.