I am sorry your baby is not feeling well
Diarrhea is caused by parasites or GI upsets or stress:
Your baby can have Immodium or kayopectate:
Kaopectate at 1 teaspoon per 5 pound every 2 - 6 hours or Immodium at 1 mg per 15 pounds one or two times a day can be given for diarrhea.
I would pick up any dog food.Try a small amount of boiled chicken with all fat drained off, chop meat , or baby food, eggs, cheese , beef, turkey, etc add cooked white rice or infant rice cereal.
Go very slow so he does not throw it up.
Dogs get dehydrated and hypoglycemic very easily from diarrhea.
Add unflavored pedialyte to his water 50/50 to hydrate him and balance his electrolytes.
Put a few drops of pancake syrup on his tongue to raise his blood sugar in case he is a bit hypoglycemic. That should perk him up.
Do not allow him to drink a lot at a time If he throws up water, he can lick ice
Keep him on that very light diet of boiled chicken or baby food for 48 hours after the stool is normal.
Also give him one teaspoon a day of plain yogurt to keep "good" bacteria in his system.
If he develops any abdominal pain, bloating, constipation or cannot keep anything down he needs to be seen by a vet.
Please let me know how he is doing. I will always be here for you
I hope your baby feels better very soon..
Best wishes for him,