Hello Tracee so sorry to hear about your boy
you say he's spent four days at the vets maybe it's been too much for him and once he's back home and re-adjusts hopefully things will settle down with him and then hopefully he will start eating again
When your animals are ill it's so very stressful for us so god knows what it must be like for them because they can't express how they feel
My dog Scoobie has been very poorly with a pancreatic disorder (his pancreas can't produce the enzymes needed to break down fats)and he will be on medication for the rest of his life and a prescription diet. It's so sad when they are ill but you have to do what's best for them and I'm sure you are but try not to worry and like the others have said have a word with your vet if he doesn't get his appetite back soon
wishing you all the very best and keep coming back to COL just for some friendly advice