I have no silver bullet.
I managed to get a Physics degree mostly from profs who did not teach...unless you call xeroxing the textbook on to slides and reading them to us during class time teaching. Their research, OTOH, got tender loving care and attention.
Oh, and the math beyond Calc required for some of the work...got to learn that on the fly, too.
Physics would be easier if you got your degree in Math, first.
Your situation sounds ugly & ominous. I would recommend buying that other textbook, giving your other classes only the attention needed to "B" them, shut off all social interaction, and spend your time hitting the thermo. If you contact your prof, have a couple of well thought-out questions that get to the point.