Trying to lose weight?

I weigh about 122 lbs on a height of 5'4" or 5'3" and 1/2. I've been working out 1/2 hour after school in our schools fitness center, with the eliptical and treadmill. I'm focusing on toning my butt and thighs. I have curvy thighs, but mostly a size 2-4. I'm always told I'm skinny/tiny when I tell people I'm on a diet (I eat no sweets until Saturday, then I can have a cheat day). The problem is, I only hear it when I tell people I'm on a diet. They never come up to me like "aw your so skinny!" and people lie about that all the time to others, so what if they are lying to me? I'm on about 1000 calories and sometimes I eat too much and (not proud of this) regurgitate.

My main question is: when is a girl too skinny? How do I know I am really skinny and people aren't just lying to be nice?
Trying to lose weight?
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