I'm sorry your baby is ill. I would be aggressive with diagnostics and treatment at this time. It is very alarming when a young toy breed dog is vomiting and can't keep food down. He will dehydrate quickly not to mention the low blood sugar that you've already been on the outlook for.
Regardless of the presence of diarrhea, I would recommend a fecal test for parasites as well as routine deworming, Snap parvo
test, routine blood work to include a chemistry panel, complete blood count and urinalysis as well as x-rays of his chest and abdomen. The x-rays are optional but advised especially if the other diagnostics don't reveal a specific cause of the problem.
Based on the outcome of the results, your puppy may need other tests. I would consider bile acids to check for liver function issues (i.e. small breed dogs can be born with liver shunts that contribute to ill thrift and vomiting) and possibly a baseline cortisol to evaluate for atypical Addison's disease which can also be congenital.
Minimal treatment would be subcutaneous fluids and injectable medication for nausea (e.g. Cerenia) which may get him back on track for 24 hours. However, based on the results of the recommended diagnostics, hospitalization may be considered for supportive care as needed (i.e. intravenous fluids, injectable nausea medication as well as injectable antibiotics and antacids, etc.). This is especially true if any evidence of viral or bacterial infection is present such as a positive parvo test or changes in the white blood cell distribution on complete blood count as well as evaluating for evidence of pneumonia on chest x-rays.
These little guys can be very fragile which is the reason for the rather thorough work-up I've outlined above. Two days of significant illness is a long time for a young tiny dog like this. It is prudent to be thorough in trying to evaluate for illness and providing supportive care.
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