How to gain self confidence?

i mean i used to be so self-confident. Then things started to happen. Im not ugly, i dont think im fat but i really dont have self confidence. Ive gotten made fun of alot and im always talked about. Jerky guys and girls make fun of my mole on the side of my face. its the size of a pinky nail. That hurts. Im often used and feel like i have hardly any real friends. I used to be this bubbly, happy all the time person. but ive changed soo much. i miss the old self confident me. Im 13.