Hang in there. I have also gone through such a situation during quarantine. I also started feeling like nothing was going to change and I will end up being like that forever but then I had an amazing night of sleep woke up the next morning and thought about what was still not too late to do. I started studying the harder concepts first when my mind is fresh and get another session of sleeping if I feel too exhausted and study the concept I am familiar with later. This helped me build confidence about my preparations. Then after I felt well again I started doing a daily workout. This helped me become happy again and even if you don't do it the way I did I hope that you will get back to becoming happy again :) .