how do you know when you've taken it to far?

i would not starve myself, but i can't stand the way i look, and what bothers me is the fact that i'm so hung up on the way i look. i'm really short, like 4 10' short, so i know i don't LOOK thin, which is what bugs me so much. I wasn't always like this, but ever since starting high school my weight has been on my mind 24/7. When i'm at school i'm constantly looking at how the other girls look (pratically every girl that passes by). I also spend a little too much time criticizing myself in the mirror. I'm worried about having a boyfriend (if i ever get one that is) because he might think i'm "chubby". It's even gotten to the point where i feel guilty everytime i put something in my mouth. I'm not depressed or anything, even though this post sounds like i am. to tell you the truth, all of this is really draining me and i want it to stop, but i don't know how.

is it possible that it could all be in my head, because my family is always nagging at me to eat more or how thin I am, but trust me I DON"T see it.