Give yourself more time, don't pressure yourself. Probably your brain will be better with more time, you are still 17 and developing. Even if it is more difficult for you now than before, it doesn't mean you cannot achieve anything you want. It will probably take you more time. Be patient, small steps to your goal is still progress.

I would try to find things that make me happy and make me use my brain, for example video games. I think it is a good way to train your brain while you enjoy, instead of watching tv or things like that. And don't forget to make some sport and eat healthy, those two things help with everything.

I am not a doctor, talk to professionals anyway (more than one).