Thank you guys for the wonderful advice. I saw my MIL and Poopy tonight, thankfully he looked much better. The medications and fluid injections have seemed to really work! Aside from being hungry, he was playful (as much as an 1 year old yorkie can be) and his regular self.
My MIL said the Vet told her to only feed him boiled chicken, rice, and cottage cheese. No more treats like Cheerios or dog treats. Low-fat foods ONLY. I guess when he was a puppy, my Father-in-law would give him ice cream! Ah! Not good.
So all is looking good and I think MIL is taking the right actions to help him.
He has another appointment tomorrow, so we're praying for a good outlook!