The general rule is to rest the tummy for about 12 hours. Immodium works much better than Pepto.
KAOPECTATE/IMMODIUM (loperamide):
Can be given to dogs and cats (1 teaspoon for every 20 pounds) for diarrhea. This dosage can be repeated every 4-6 hours for 24 hours, or until symptoms begin to resolve. OTC Medications
Try to keep him hydrated by giving him droppers full of Pedialite. After his tummy is rested, try a little bit of boiled chicken breast and rice, just a spoonful at first to see how he handles it.
Dehydration is the biggest concern with these little ones. It is amazing how quickly a six pound dog can dehydrate from vomiting or diarrhea. If he doesn't improve quickly and still acts lethargic, you need to get him to a vet asap for fluids. Electrolyte imbalances from dehydration are very serious and can even cause cardiac arrest.