Well I think the reason he gets short bursts of energy is because he's still very much a baby. They get tired out very quickly. Puppies before 8 weeks of age aren't really ready to be away from their mothers, so since you got yours a little bit early I'd just be careful to make sure the puppy is getting all of its nutrition.
I like Canidae ALS as the dog food I use.. but I also know that Innova is a good one too.
I have a yorkie poodle mix also
They're so much fun!!