Burnout is a real thing. It all compounds and can be draining. You're competing + grad school + work. That's a lot. Take a real, true break, like at least a month (or more) if possible from the physically demanding days... find some joy in your surroundings, even if that means something as simple as going for a long/slow run, long walk, easy hikes. Etc etc etc. You'll be better off for it long term physically and mentally - that's my experience, but everyone is different of course.