If you are in the USA, you are protected by HIPPA regardless of your age. HIPPA is the law that keeps all your health information private. Unless something is life threatening or you are threatening someone else's life your T should not be able to tell anybody (including your parents) anything concerning your health (or whatever you may disclose with him/her) without your permission.
Look up the HIPPA law. If you are still uncertain, then ask your T for a copy of their Privacy Policy and if that is still unclear, then ask your T what kinds of things they have to report to who and when.

Be well,

Celtic