It could possibly be a result of a dietary sensitivity. Many dogs experience similar symptoms as a result of a sensitivity to meat products. Nature's Recipe is one brand of dog food you can buy at any pet store, and they have an allergy formula made specifically for that (it's vegetarian and nutritionally balanced). There are several other food options, but I would personally try that first rather than go the medication route. This is obviously a symptom of a problem of some sort. If you do switch his food, be sure to add in some of the new food every day and gradually ween out the old food to prevent stomach upset. Good luck to you both and I hope this helps!