My heart breaks for you and for your late little Louis.
Two articles on YorkieTalk helpful to all pet parents, both are in the same thread:
These pups are tiny, tiny little ones. (Many human babies weigh more than our adult pets.) Things can go south or get better very quickly.
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When to take your dog to the vet immediately."
I lost my sweet senior yorkie, Katy, at the end of March after a long illness. I'd have to think back, but at this writing believe essentially all of my "call in" questions to the vet concerned post treatment questions. There were times I asked for a tech visit--just to have a professional take Katy's vitals.
Thoughts and prayers with you.