OK so my "friends" call me bipolar and I just take it as a joke. OK so you have to know that our group of friends is big like 7 in our group. We are all going to different high schools and I'm the only one going to my high svhool. They always go out and do stuff together and I get mad cause I'm not invited. And I talked to my supposed best friend and she just defended her self saying it was a last minute thing to get over some drama we had. OK good so far? no... so this girls invited EVERYBODY I mean everybody in our group to her party and I wasn't invited.
They talked about me behind my back all my friends said that they do not invite me places because I have mood swings and I'm a "downer"
Should I be left out for being a downer?
I'm a downer becausse I'm left out!
Should I completely ditch these people?

Sounds like they already ditched you, does not sound like there is anything to ditch, perhaps just face the truth that after going to different schools it is time to make friends in your own school

I think these people are not your friends if they treat you this way.. you are better off staying away from them. However, if you do have issues with severe mood swings and often feel down, maybe they see a different side of you when you feel that way. You should talk to someone and maybe you will be able to find ways to manage your emotions and feel more balanced. I am sorry that this is the way they let you know, but if you can learn from it.. then maybe you can become a happier person.

Yes you should completely ditch them. They are hans down not your true friends. True friends do not leave you out of things. True friends do not talk about you behing your back. True friends care about you. They don't care about you at all or they would not be treating you that way. Get rid of them. You do not need them. You can always do better.