Sorry, didn't have time to read all the posts.
To the original question: this happens to me a lot. I never go to the bathroom at school, because it's horrible to have to use a girl's bathroom. In our PE locker rooms, everyone looked at me funny on the first day, but I guess they figure I can't be a guy in the girl's locker room, for a couple reasons: 1, I had a locker to open, indicating the teacher had given it to me verifying I belonged there, and 2, I had to get undressed in front of all of them, and I don't think that anyone could argue that I'm not a girl after seeing part of my huge boobs. And although all these reasons make me mad, at least they don't all stare anymore.
I guess I would just ignore them, and if you can, train yourself to not need to go to the bathroom during school time.