Why do my friends treat me like dirt ?

so , I love my friends to death and everything , but when I wear short shorts to school ( that arent even that short ) they yell at me , when almost every other girl wear shorts WAY shorter than mine , and they NEVER yell at them ,
Whenever I try to give an idea or something ,they’ll turn their noses up and say their idea is better , & its really annoying , they do that with everything .

& me and my best friends boyfriend , alex , are best friends. me and him decided that we were gonna be brother and sister , so we put our names together on msn, and she got mad at me because she thought I was flirting with her boyfriend. but I clearly wasnt , because for one we’re best friends , and thats it.. and for two , I already have an amazing boyfriend , Andrew ♥ So my friends get mad at me for everything , they block me out of everything .. if everyone is going to someones house , they wont invite me .. if I call them , they wont answer cause they “ are busy” when I know theyre not. If I try to sit next to them , theyll squish together and make me sit alone.. Like , theyre nice and everything , but they always act like this ^^ we’re so much alike , and I would be so lost without them , but I get so annoyed when they treat me like this . some times theyre nice and they let me sit with them, and the like my ideas , and they wont get mad at me for no reason , but usauualy , they do.

I’m popular and everything (not trying to be a snob) and a lot of people like me and everything , but they just seem to hate me . & I know they talk about me behind my back and stuff.. and I dont know what to do about it , because whenever I try to talk to them about it , they end up getting mad at me , and hating me even more.
ADVICE ? <3