Well my brother the first thing you have to do is realize the fact that you are doing extraordinary things. Not everyone is willing to put in so much hard work, so pat yourself on the back for that. What you are doing is not easy, not one said it was supposed to be easy, but think of it as a seed that you will plant which will flourish as time passes and as you finally graduate with a smile on your face.
The best thing you can do for yourself is learn how to manage your time, and, see if you can, after learning when to study for this topic and when to study for that topic, is to see if you can have some relaxation time, even if just ten minutes, take a break, take time for yourself, and take it easy on yourself.