I am extremely passionate about entropy/physics, but I don't think I can get into grad school. What can I do to pursue these topics sustainably?
Passion will not make you a successful PhD student.  Health problems will prevent you from being a successful PhD student.  

I suggest you find a job that is relevant to physics.  Considering your interests and the current job market, maybe a job in data science?  Demonstrate over a period of at least a year that you can be successful at that job.  Study for the Physics GRE and get a GRE score.  Then you might be able to get into a decent PhD program.

Enjoying studying entropy does not mean you will enjoy publishing about it; these are quite different activities.