I've been using avamys in high doses and taking allegra (fexofenadine) 120mg daily for months but still I get sore throats at least once a month. Some end in the flu.

Well. First are you using your avamyst correctly by aiming the nozzle outwards inside the nasal cavity? If not, the medication may not have reached the right area to work. Another possibility is that the nasal symptoms have nothing to do with your sore throat.