I'm sure some on this forum can help if you give more details.
How long has the problem being going on for?
What type of diet do you feed your dog?
Are there emotional issues that might cause this? (like anxiety?)
Although some recommend yoghurt, I don't resonate with that. Dairy is not really suitable for animals, so you might want to look at a canine probiotics supplement.
What makes you think it's a yeast problem? Has he had Antibiotics ? Do his snacks/food contain sugar?