How can I be more confident? Girl 14?

[Fiona]

Hi my name is Fiona, I'm not that confident. I look in the mirror and hate how I look. I hate my face, my hair, my figure, my legs, my nose everything. When I'm in school I get really really shy when I'm talking to people in older years.. I get all nervous and shaky. If someone gives me a bad look i take it to heart. Especially walking past the 3rd year boys just really makes me shy, and I don't really know why. When a boy teases me or something I smile and look like an idiot. where as other girls just act cooler around them then me. I just get really fidgety. I'm like a year and a half older then them, and I'M the one getting nervous :'(. I hate my figure so much, I'm like a stone and a half over weight. I'm trying to except my self for who I am but thats difficult. I tried to diet and exercise more... but that just made me eat more :'( i had a bad breakup which made me feel more like shit. Now I find myself comparing myself to every other girl I see. I find myself going onto facebook and looking and girls profile pictures. and ones when their with their friends. And they're so pretty. I don't have many friends, but I do have people I trust. And I know the quality of friends is better then the quantity. Please help, I just want to be more confident in myself. HOW? I'll chose best answer :') Thanks, truly appreciated :') x