Definitely check with your vet.
I have a male lab mix named Riley who was having similar problems last spring. Before running a bunch of tests, my vet recommended trying a different food, and what she recommended was Science Diet Oral Care--nothing majorly scientific except that she said it was known to "constipate" dogs sometimes, and that was sort of the effect we were going for.
Sounds strange, I know, but we tried it, and he did very well on that food.