Hello,
you do not name the breeder, but from what you say, I have certain idea about its possible origin. If I am right, ask the veterinarian to run tests on herpes virus. Also ask the veterinarian to run tests on the diarrhoea, to check the bacterias and possible manifestation of worms. The puppy probably needs antibiotics, possibly it will need to be dewormed. But do one thing at a time.
Do not let the puppy eat his diarrhoea. Keep the puppy on diet - best is boiled chicken with rice, forget about the dry food, it will not help. First you need to fix the diarrhoea, then deal with the lack of vitamins. Rice and chicken with help you stop it, together with the proper antibiotics. Then when the puppy feels stronger, you might start adding more things into his diet, or go slowly to dry food diet.
Your puppy is in serious problems, it is not normal for a puppy to be sick like this and the breeder should be exposed for breeding and selling pups in this shape, whoever it is. However, who sells puppies in this shape, probably does not care about them and their fate. You might not see your money back, and they may refuse to take the puppy back. Sorry, it looks like you bought your puppy from a mass producer.
