How can I change myself?

I'm 16 and have been bullied throughout my life for being different. Also my family is kind of poor and I do not have the things that the more popular girls adore. At my present school I was a late starter (because I was physically very badly bullied at my previously) and although people were nice to me at first, a vicious rumor was spread by someone (apparently i slept with her 'popular' boyfriend) and the entire year will have nothing to do with me now. Someone once filled my locker with condoms (some used) I am always partner less in games (when i do get paired up, i get baseballs and other things thrown at me), people steal my things and I've taken to eating lunch in the bathroom as people chuck food at me. I've never had any friends and am an only child.Most recently, i accepted an invitation from one of the more popular boys in school to prom (apparently he thought i should have a good time for once), turns out he did this to make fun of me as he already had a date and told the rest of the year about it. That day i stood alone in the corner of the room for half an hour, after this I left the school for the quiet of the grounds were i sat for the rest of the evening. Later i was greeted by people honking and laughing at me through their cars (I had to walk home). My grades are poor no mater how hard I try and I am always very ill which again people make fun of me about-and i may have to retake the year. I think that something must be really wrong with me for this bullying cycle to happen continually. How can i become cool/at least normal so that people will at least respect me as a normal Human for once? =(