The Claritin and Zurtec can dry him out terribly so always try half doses. J had horrible bloody noses when he took it.
To my way of thinking:
If it's runny and the eyes are watery, dripping nose, clear goo only, no coughing, it's allergies.
If it's thick, colored, smelly breath,coughing up colored stuff, etc...it may need an antibiotic.
It they are having stuffy nose the REAL Sudafed, from the family style Pharmacy, not Wal_greens or Wal-Mart, REAL Sudafed will help with that. It will also help with the allergy reactions because the nasal mucus is runnier and it will wash the allergens away quicker.
I would think an ENT would have done a sinus X-RAY first visit, plus be able to say for sure if the allergy testing was valid. If he had any allergy medicine in his system for a week before the testing he did not have an accurate test. The allergy medicine did not allow the allergen to cause him to react.
When I did allergy testing the allergy doc told me no antihistamines for at least 8 days before testing. I reacted to 74 out of 80 things I was tested for. The tobacco swatch on my back reacted and swelled up to about 6" across.
I only had 17 things tested again on my arms, where they put a tiny amount under the skin, and almost everyone of those reacted.