My puppy has had diarrhea...?

Spencer is a very sweet 4 month-old chocolate lab puppy who is a great dog, but lately he has had diarrhea. After several visits at the vet, we determined that it was an internal parasite. We got diarrhea pills and parasite medication. He finished his dosage of the parasite medication, and he was 100% normal, so we laid off the diarrhea pills. two days later, he had diarrhea in the evening, even though he was normal throughout the day. He threw up a plant once three days ago, but was fine after that. He is too young for rabies, so could he have eaten a foreign object or have a disease? Thanks!