We have the same problem. After going to several vets, trying various medications and food, we've discovered that our dog has atopic dermatitis with a superimposed bacterial and malassezia infection (yeast). We are treating her with a short burst of steroid, simplicef for the bacteria, and ketoconazole for the yeast. We also use Malaseb shampoo twice a week (use cool baths, not hot water, and let the lather soak in for a good 10 minutes). She is on the Z/D Prescription diet (ultra-allergen), but the vet thinks that she more likely has atopic dermatitis rather than food allergies. Once her infections are cleared, we're going to try Atopica (a cyclosporine) for her.
It's a lot, but I think once you get it under control, it's just a matter of maintenance. I'm hopeful that the Atopica will help prevent the itching, which leads to infections, etc.
It also helps to wash the dog's leash and bedding with hot water/chlorox frequently.
Hope this helps! I learned all this info from our fabulous new vet and technician. There's nothing worse than a miserable pug.