Are you my twin, separated at birth?
Seriously, exact same situation as me. This girl that I like and I don't often have much contact, but she sometimes gives me compliments (For example, you're so smart, so funny, etc), and we often lock eyes, and she sometimes gives me other IOI's too. Only weird part about this that makes me think that maybe I'm misinterpreting something is that she's one of the most popular girls in school and she's beautiful- whereas I'm pretty low on the social food chain, and I'm not exactly physically attractive, either. She's probably the nicest person I've ever met, and I'd be ecstatic if I found out she liked me, but I won't get my hopes up.
Anyway, we're in the same boat, man, so I don't know if I can offer any advice.
I would greatly appreciate any help with my situation, as well.
Edit: another thing I forgot to mention is that, somewhat like your situation, she's ALWAYS, without exception, with someone. I can never catch her alone, ever.