Am i fat? i'm 5'7" and 120 lbs?

At 5'7 and 120 pounds you really don't need to lose more weight--you're already at the very bottom of the acceptable weights for your height. My girlfriend is 5'7, 140 pounds, and she looks great! 120 pounds is a perfectly good weight but don't lose more than that. Having some curves is just part of being a female, you don't really want to have a completely flat butt and no thighs, very few people find that attractive.