I’d say step one is to lower the bar and give yourself some grace. You are to be congratulated for putting yourself through school. It’s hard to work and go to school, and so you should be proud of that. So, one way to take care of yourself is to make sure you are forgiving yourself for not being able to do all that you want to do. One day, you’ll be done with school, and you’ll have more and more opportunities to do fun things.
I’d also suggest you write out a short list of things you’d like to do for fun. Maybe it’s reading a book, or developing a friendship, or going to a concert, etc. Then, put those on a calendar just like you do for your work hours or your classroom hours. If necessary, take a day off now and then so you can do what you need to do for yourself.