Do you live in the US? If so, you have the legal right to an assessment by a Speech-Language Pathologist at your school who can help you get the help you need. PM me if you need help, I work as an SLP at a high school and work with several high schoolers in the same boat at you. We are here to help and support you. I know you said you've tried lots of therapy, but an SLP isn't just for "therapy" - we can help communicate with your teachers so they know what's going on and help connect you to other kids who stutter and support groups in your area.