Should I tell my mum?

I've told my mum many times that I want to move back to cornwall. She sys we can't cuz of my dads job. The main reason I want to move back down there is because most of my family is down there. At school I have had quite a few best friends, and I have one at the moment but she keeps going all quite when it's just me around and when ever she's with this other girl she's always laughing and that. Randomly all the other girls in my cl don't seem to like me so if my best friend isn't my friend anymore, who do I have? I think part of the reason why people don't seem to like me is because of my sister. she has gone out with loads of boys and whenever they or she ends it she's always going out with someone else the next day. People call me a slag and slut but I'm nothing like my sister, iveonly had one proper boyfriend! I really wanna make a fresh start where I belong as I don't really fit in here. But whenever my mum asks how school was I say it's fine when really it's not. Help? Should I tell er the real reason because we would never move without telling her the real reason. She asked me if I wanted to move schools before because she felt sorry for me having to put up with all this about my sister, but she only said I could move to a school nearby no where near where I belong. I really don't fit in. :'(