this may too be late for your use, but maybe someone else can find it useful. We had a weimaraner that also had allergies. We didn't find out until she was about 9-12 months old. Until then it was chronic ear infections & hair falling out. We had comprehensive allergy testing done, and found out she was allergic to (among other things): house flies, mosquitoes, oak, and flour.
So what did that mean? getting Flea, Tick AND Mosquito repellent. Keeping her away from sticks in the park. Trying to not allow her to eat flies. And finally dog food with NO FLOUR. At the time, there was one option, I believe it was Nutro or something similar. Eventually we found Drs. Foster and Smith brand food, which has no flour. She ate Dr. Foster and Smith food for 10 out of her 15 years.
Get your dog allergy tested. find out exactly what the problem is. It's expensive, but not as much as monthly vet bills.