Get Your Dog Care Questions Answered by Experts
There are a lot of causes for diarrhea in a puppy. The first and most scary is parvo. With parvo, you might see diarrhea with blood, vomiting and all over weakness. This is a deadly disease so you need to see the vet immediately if you suspect this.
The other cause might include a parasite problem and the puppy needs to be dewormed. Coccidia and other problems are often overlooked.
You need to see the vet tomorrow for a fecal or a parvo test.
Let me know if you still have questions.
They need 3 rounds of vaccines at 3 week intervals before they are protected from contagious disease. So, you did great by vaccinating him but he is not yet fully protected so this could be a cause.
It could also be coccidia or a parasite that was undetected earlier.