Have you talked to a therapist/psychiatrist? I went through a period of being extremely unproductive and depressed and was diagnosed w ADHD shortly after that—could be worth exploring! Otherwise I rely on time pressure/adrenaline to get stuff done (terrible advice) and thinking about setting small goals every week—eg go to bed before midnight, do 30 mins of work when you wake up, etc. also trying to work somewhere different (library, coffee shop, etc) or with friends. Start small—studying 30 mins is better than 0 mins, so make that your goal to start!!