I had the same problem with Lily. YT was a lifesaver for her.
Try this recipe that someone here gave me. It helps keep their blood sugar up and they really seem to like it. I showed it to my vet and he gave it a thumbs up
1/2 cup goat's milk
1/2 cup Gerber rice cereal
1 jar of Gerber's baby meat (I used beef)
1 tsp. karo syrup
It originally used half and half but I replaced it with the goat's milk because the half and half tended to cause diarrhea. After a few days, you can start to add ground up kibble or canned dog food to this. Each day you can increase the ratio of dog food to above recipe until you are just feeding the dog food.
In Lily's case, I also gave her a liquid supplement called Rebound that you can get at the vet's office. This gives them all the nutrients and vitamins they need.