I have no self confidence?

i go to an all girls school and well u no how it is we get really bitchy and horrible and judgemental i hate it i am shy and pretty much invisable i cant stand fallin out with people cos i am terrible at it. People are fake in my skwl and judge me without really even knowin or tlkin to me . My question is how do people get confidence? and i know u cant get it easily you have to think about being confident and not caring about stuff but i try that all the time and it just makes me care more :( i love to laugh and i love to make other laugh and i want to have the confidence to be able to speak to people and not look petrified or speak in a voice too quiet for them to hear. and to also not give one about when people talk about me or *****. any help on this would be great thanks xx