Sounds like classic symptoms of hypoglycemia, and you were right to give the Nutristat, but it’s good to give them food within 20 minutes of giving the Nutristat. Does he have all his baby teeth, is he having a problem chewing? He may even be younger than the vet guessed. You could try softening up a little kibble or giving some boiled chicken. If the puppy is continually getting hypoglycemia, there may be a low grade infection. Here’s more information on hypoglycemia, but I think the vet you work with should be notified about this.
Toy Breed Hypoglycemia