What Causes Persistent Post Nasal Drip In A Child?

Hi my 6 year old has had a stuffy runny nose for about a year, he does not respond to nasal steroids, and Astelin and antihistamines. he snores loudly at night and demostrates symptoms of OSA. He does not respond to oral decongestants but responds to Afrin. he is normal weight. His tonsils are small but his adenoids are hypertrophied based on two Xrays however because they do not block the nasal cavity the ENT physician is advising to keep the adenoids and consider terbinate surgery. The blocked nose has significantly affected his quality of life and we are desperate to find a solution. I am concerned about the surgeon only wanting to do a terbinate surgery. he was scoped for 2 seconds before my son yanked the scope out, and the surgeon said that he did not think adenoids are problematic. However I am doubtful he actually took a good look because it looked like he did not complete an insertion. My son also has developed an underbite and he salivates profusely. He is chronically breathing through his nose and his speach is hyponasal.