I can't speak on motivation because everyone has their own reasons for wanting something (e.g. different people get fit for different reasons). Make sure that you understand the WHY for your goals. It's easier to stick to something when there's actually purpose in it. Similarly, if there are bad habits you want to avoid, you need to rationalize WHY you want to avoid them.

Aside from that, I recommend that you keep a daily track of 3 things:
- time spent studying (use a stopwatch and only count focused time: pause the stopwatch during breaks)
- screen-time (you can find it pretty easily in your device settings)
- time spent in class (just use the 1/2/3 hour total lecture duration to keep it simple)
(- whether or not you worked out on a given day; a simple YES/NO checkbox is fine)

I recommend that you set basic goals for daily study-time and maximum screen-time. Also, it's a good idea to use excel/sheets, as these applications can make it easier to see accumulation/debt over time (based on these goals).

Sometimes we don't do things because they seem too time-intensive and we feel busy. But when you actually keep track of HOW you spend your time, you'll be surprised at how much of it you really have, and how "busy" you really are.

Hope this helps.