My girlfriend is driving me insane.

Okay, well I have a girlfriend 3 years older than me. She's a senior and I'm a sophomore. I thought I really liked her, I still do, but today she's expressed a different side of her to me. Turns out to me that she has a slutty side to her, she told me once she turns 18 she's letting her friend take her clubbing, and she said she was going to wear high heels and a "nice" outfit to dance in. She completely ignores me when she's talking to other guys, and leaves me sitting there looking like a dumba$$. She's always flirting now with other guys, and I got mad at her today and she can't understand why. Jealousy is always eating me alive, but the fact that she just ignores me when she's talking to other people is just rude.

We've been dating for 2 weeks now and I'm already kinda annoyed by her. But should I wait longer and see how it goes? Or just not waste my time on a girl like that?

maybe because you just started dating, she hasn't really 'committed' to you yet, and maybe if you give it more time the flirting will stop, or at least occur less often.
it could also be that she's trying to see how far she can push you before you get, which happens often at the beginning of relationships... she may just be testing you.
or, it could be that she feels you aren't paying enough attention to her, and is trying to make you jealous.
my advice would be to talk to her about it, but don't yell at her or accuse her of anything. say something like 'maybe its all in my head, but it feels like you ignore me when we're in groups and flirt with other guys.' or 'I feel like you'd rather be with [name] and [name] than me whenever we're with them.'
use 'it feels like...' or 'it seems like...' rather than 'you are...' because that will only make her mad and defensive.
hope it works out!