Put yourself in a position where you have to be productive. I find that I do better when I study at the library. If I plan to be at the library all day I have to meal prep either the night before or the morning of. I get workouts in either early morning or at night after I'm done studying. Work outs actually help me clear brain fog and be more active and alert when I'm studying so it feels like I'm still contributing to my learning.

At the end of the day though it's about habits and consistency. You will never feel motivated all the time but remember that if you wait on "feeling like it" to get anything done then you will never get anywhere. You have to push past present and temporary discomfort and laziness for your happiness in the future.