Maria:
It's hard to understand why the vet didn't give Major some sub-cutaneous fluids. His condition may not be bad enough to require an IV, but certainly he should have had sub-cutaneous fluids. It would be painless for him, but would do him a world of good, since he hasn't been drinking much.
If he doesn't start drinking normally, please take him back to the vet ASAP for sub-cutaneous fluids. It is painless; they just inject it under his skin on his back. It makes a big "bump" for a while, but in a short time his body absorbs it.
If Major becomes dehydrated, his kidneys will fail and that can be deadly and he can reach the point of no return very quickly!
He should be in the house, too, so you can sleep beside him to watch him and know if he's drinking anything. Sleep on the kitchen floor with him if you have to -- do whatever it takes!
I usually just "lurk" on Dog of the Day, but registered just to be able to write to you.
Dorrie