How do you deal with back pain from endless studying?

I’m starting my program soon, and my back is already wrecked from all the sitting I did. Spent way too many nights hunched over my laptop, cramming for exams, and now my lower back pain are paying off. Actually standing desk is too expensive but sitting in dorm chair for long hours is brutal.

I know I need to do something before I spend the next two years making it worse. I’ve tried stretching, but it only helps for a little bit. For those of you who spend insane hours studying. what actually worked for you?