Perhaps you should look for a new vet. When you say "loose stool" is it really runny like watery or is it soft? Have you the pumpkin like Dvlish suggested? It usually helps with loose stool. Also, while you're trying to decide on the right food, perhaps boiled chicken breast would be good? It's another form of "bland diet".
If you haven't looked at this already, here's a link on ratings for dog food.
Dog Food Reviews and Ratings | Dog Food Advisor