
I'm surprised that the breeder didnt give you details of when he was wormed this has to be continued and usually the vet will give you the tablets and information with his vacinations.
Worms can cause diahorrea and sometimes they can vomit them up if badly infested.
I personally would change to a dry food as I dont like bakers or Pedigree but that is my choice I feed Arden Grange.
You need to visit the vet for worm treatment as over the counter is of no use in my opinion.
Starve for 24 hours and then chicken and rice in small meals for a day or two then wean him back onto your chosen food.
It can be difficult to starve a young pup so I have been known to give a little dry cake or arrowroot biscuits to take away the hunger pangs if necessary.(advise from my vet)
Roni