How do I focus without using brain drugs?

I've tried music. I've tried complete silence. I've tried chewing gum. I've tried studying in groups. I've tried studying alone. I've tried studying in a library. I've tried studying in a cafe. I've tried the Pomodoro technique. I've tried watching a lecture given by an awesome teacher and then stopping the video to do the 20 or 30 problems for the day. I've tried everything I can think of or find on the internet and nothing works. I've been to the doctor and it's not ADHD. I need to study but I can't.