Years ago I had 2 pups left that had had 2 shots,almost due for a third. At a birthday party at my house a child came whose dog had just died of parvo days before. Of course there is no mention of this until AFTER my bablies got sick. Days later he t...

Have the vet examine him. At the age they go downhill fast.
It could be just what you mentioned and even more so in a large litter...but it also could be worms or other more serious illnesses right up to Parvo. It is not worth losing the entire ...