yelping in pain concerns me and the walking off balance.
Did he have vaccines recently like within last two months?
I would not mess with this if dog is in pain and get him to a specialty hospital where there is an internal medicine specialist and neurologist.
The blood work is not really way off so this could be neurological and dogs do not yelp in pain unless they are in alot of pain. I think this is out of the hands of a normal vet and your dog needs to see a specialist to figure what is going on.
They will need to rule out liver issue along with neurological issue. Please do not wait go as soon as you can as your dog is in pain
and if it is something neurological like in the spine then the sooner your dog is treated the better. I think you have a vet school near you so maybe check there as may be cheaper
my gut is this can be neurological related as liver disease dogs do not yelp in pain and your dog is not vomitting or having diarrhea so do not think digestive issues. I just think a specialty hospital or vet school has a team of doctors to figure out quickly what is going on so that is what i would do if it was my dog. This is not something to take a wait and see approach in my opinion when a dog is in pain.