Therapist wants me to go to GP but parents don'tWatch
What are you scared of?
However, I understand your issue. I’ve never received much sympathy from home for similar issues. I was also encouraged to call a GP, and so because of COVID I had to call over the phone. Maybe try call during school hours so your parents don’t know? The queues are long, so if you call first thing in the morning many GP surgeries have an option to have them call you back once you’re first in the queue. If you let your teachers know you needed to possibly leave for a call at some point, would they let you?
This might have been far more detail than you wanted so I apologise.