My girl was diagnosed with HGE about a month ago. Same type symptoms and come to found out, yorkies are one of the breeds it is more common in. Just google HGE (
Hemorrhagic GastroEnteritis ) in dogs and you will see lots of info. Basically it's a virus and they don't know how they get it. I had never heard of it until it happened to us. Treating it quick is the key. Ginger is back 100% - no more issues. Sounds like you got your baby in early too! Hope he is feeling better!!!!!