I've been having sex with this girl for about a month now. She will sometimes say that we're going out exclusively then turn around the next day and ask what we are. This is very aggrivating... I've been told by several people that she doesn't know what she wants, including her mom. I really like her and serious feelings are evolving but I don't want to get hurt. I'm not sure if I can trust her around other guys either, especially after she's been taking Xanaxs and drinking.

Should I just keep fucking her and go with what I think it might be (her having fun), totally forget about her (hard to do), or try and build a relationship?

Only take the relationship as seriously as you think she is taking the relationship. If you feel she's stand-off-ish, then you be so. If you get stood up one night, do the same to her.. From the little detail I have of your predicament, I'd say she's more in need of some comfort, a crutch. She needs something she knows will be there so that she doesn't feel on her own.. But hey, what do I know? Talk to her. If you don't get anything out of the conversation, then you prolly won't get anything out of the relationship. Be mature, use your head.