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It sounds like he may indeed have allergies. Unfortunately, antihistamines only relieve the symptoms temporarily. After you use it for a few days, it can actually irritate the eye more. For allergy flareups, I usually start patients on a low potency steroids (like FML) for a few weeks to get over the acute symptoms. At the same time, I start them on a mast cell stabilizer (like Crolom or Pataday or Optivar). These drops can be used chronically. They serve to decrease the frequency and intensity of flareups.
Sometimes, when the symptoms are severe, systemic medications temporarily can help also (such as Zyrtec, Allegra). You can also observe your son in his environment. If some activity or place seems to worsen the symptoms, he may be allergic to something there. Also humidifiers may help. I recommend that my patients also avoid ceiling fans (especially while sleeping).
I cannot truly comment on the proposed surgery since I have not examined your son. If he indeed has symptoms of blocked tear ducts, then surgery to unclog them may help. Usually these symptoms include tearing and mattering.
Hope this helps.