Poor little Diesel! At least they finally got to the root of the problem. It sounds like he's on the way to recovery. Is he eating now? Just a suggestion...I know your breeder suggested that you feed him Little Ceasar's, but you may want to look into a better quality food for him...especially since he's been so ill. If he's eating canned, Blue Buffalo is a good canned food & it's available at Petco/Petsmart. Blue Buffalo is just one example of a better quality food. There are a lot of brands out there. Here's a link to a website with some information about puppy food:
Best Puppy Foods
Good luck! I hope your little baby continues to get stronger & healthier! His pictures are absolutely adorable! He is such a cutie! No wonder you're in love