It is hard and a lot of of teens go trough that but you only have to look in the mirror every morning and say 'halo beatifull ', it works! just do that every morning 'till you feel that you are thinking more of yourself than you did before.......
Just don't think to much of yourself that you forget the other people around you......because that can also cause other people to think less about themselvs so just ignore the boys or the girls that brings your self-conscious down......
love yoursef and the people around you!!!!!