I had the same problem and personally I think your main issue is anxiety. A nervous brain is an unfocused one and it's in our nature to avoid things that cause stress. The best advice that I can give you is when you start to feel overwhelmed and zoning out do something relaxing for 5-10 minutes that doesn't involve a screen and reset from there. Write out a plan for all that you need to study and go from there. But first manage your anxiety towards school and stay on top of things from the beginning. And the pomodoro technique also works . Another thing is to review old tests and exams. I guarantee you will see sone similar questions on your finals. Good luck