I would get a copy of any and all bloodwork to keep in a file at home, so you can learn about what is going on.
If the immune system is suppressed enough, you will not necessarily see a fever.
I have very mixed feelings about some vet schools, as they have difficulty thinking outside of the box, still might be worth having a conversation with Dr. Holland, but you want to have a copy of the blood results in hand when you do.
This type of cancer is terrible, if it were cancer, and has a genetic component, though most likely triggered by environmental factors. My boy was a GSD, and GSDs and Goldens have the highest incidence
I am hoping for infection for your boy!
That there are no spots on the tummy, and gums are good color, I would be inclined to try to go with a lower dose of pred as soon as possible, to let the antibiotics do their job. Many vets will first decrease the doxy and keep the pred when they don't need to, which can be a fatal mistake.