I am so sorry that happened to you! I understand why she informed the headmaster if she was not in the loop, but she had NO right to tell your classmates this. In fact, isn't that against some kind of law? (well at least in the states, I know we have something called HIPAA law which prevents Health info from being spread like that...I'm not a lawyer or anything, so maybe it doesn't apply here, IDK.) Regardless, the teacher should not have commented like that in front of your class.

Maybe you can talk to head of year, as carrie ann suggested? Can you switch to a different PE teacher/class?

I wish you luck, please, please keep us posted, and def keep posting here. I agree, if you need to talk, no judgement!