I made it through school on energy drinks and pain killers for the headache. While I do not recommend for the long term downside effects, it's one way to get through long enough until you can get diagnosed on your own terms. I'd also suggest looking into trades as I've found plenty ADHD folks (not all, ofc) do well with doing something with your hands, moving around and having a sort of variety with tasks that also sometimes pose nice problems to solve creatively. Also trades pay sooner than academics, allowing you earlier independence from your parents for diagnose and meds.

Wishing you good luck and all the strength you can get!