Take speech classes!!! If you can learn to speak in front of a group of people and feel like hot sh*t doing it, then you will have mastered your confidence and no longer care what other people are thinking. Nothing improves confidence better than putting yourself out there or seeking a leaderhip position.
Well, try to not let other people opinions of you matter. When you're in a room full of people act as if their not there.... And maybe do something a little different w/ your appearance..... I hope some of this is helpful to you. Good Luck.