I am having the same problem with my Ozzie and he's 9 month old. The vet said it was hormones and prescribed a Bactrin type antibiotic. It has not cleared up completely but is better. I have had him on Fromm chicken and vegetable for about two months now, because previously the breeder had him on Bill-Jac and I didn't know any better initially. I also introduced the salmon and vegtable for a change and his breath smelled fishy. Could it be allergies or is it raging hormones since he has recently started marking on occasion?