My great dane seems in perfect health other than that he has had diarrhea for a few weeks now. He has been to the vet, and although with a stool sample, they could not find any eggs, he was treated for whip worms. He still has one more dosage to take, but seems to still be having diarrhea. I am not conviced that this was the problem.

Any ideas? This all seemed to have come on after he was vaccinated for leptospirosis. He also seems to spend a lot of time licking under his tail.