Why does this girl do this (please help me)?

Ok first off she's not being mean she is going out with you so she obviously likes you and if your not sure ask her if she does. Her calling you things like that is just a normal girl thing and shouldn't be taken seriously. It sounds as if you are young and that's how younger girls act they get tired of things real fast and all you have to do is keep it interesting. The whole i love you thing to other guys is probably because she likes you and would think it weird to say it to you, i've done it before. Look just don't worry so much grow some cajones and tell her how you feel or get over it.