Why am I so insecure about what others think about my personality?

Girlss and Guys gimmie sum help here - I'M WASTING MY LIFE BEING UPSET ALL THE TIME! I'm 15. Bitchy girls absolutly do my head in. I recon girls ***** when there insecure yeah? Thing is i dont seem to deal with it like that. Instead i curl up at home listening to coldplay in a puddle tears lol. jOK well i worry all the time about what my school friends think of me. I'm not insecure about my appearence i just think that everyone is like laughing at me because i never stick up for myself. Well, i'm probably too nice for my own good i have an issue with a certain girl - whos supposedly a mate but i hate her f ing guts- when shes around i feel as if i'm on show for her. she always trys to get one up on me all the time and shes always having a dig. Do you think its all her fault that i hate myself? Why is she doing this ITS BEEN GOING ON FOR 2 YEARS! What should i do about it cuz ya kno she finks shes well ard - but she knows i'm scared of her :( is this a form of bullying?