Hm. How to answer this.
Its hard to tell you what exactly is making people treat you the way they are, seeing as we don't know you personally. It could be just fickle teenaged behaviour (best friends one week, next week you're enemies...wtf), or it could be that you are extremely hyper sensitive and are reading way too much in the way people act. Just because a person is super friendly to you one day doesn't mean they hate you.....maybe they're having a shitty day and you just happened to say 'wazzup' at the wrong time...who knows.

I knew a few guys in hs who acted a lot like you describe yourself...outgoing, always trying to get a laugh, wearing strange things to school. Nice guys, but honestly there's some days where you just felt like saying to them "Can you just be serious or chill the f$%* out for one second?" Not everyone wants to be 'social' 24-7, and there's times that humor or the whole 'class-clown' thing is obnoxious and not appropriate. Check yourself from time to time. Be yourself, but don't go overboard because you think you won't get any attention or that people won't like you if you're not constantly 'on', f you know what I mean.