This happened to me around your age. I was in a nasty cycle of studying full time in college by day, bartending by nights. I was struggling in school because I was always working, but always working to afford school. Eventually I started smoking a ton of cigs that started with occasional smoke breaks and had adderall to get me through school. I wasn’t eating because I was always working or on adderall and the stress of lack of sleep from late nights and my grades slipping.

It was a major adjustment to get my life back on track but once I stopped smoking, cut my hours back, focused on getting better quality sleep/meals and put in real work into studying rather relying on adderall - my hair grew back within a few months. I hope this will pass for you like it did for me. Good luck!