The trick with allergies is a preemptive strike, that is getting your arms around the symptoms before they knock you out. I have allergies that can cause me to feel very viral, running a low grade fever and so on. I have gotten to the point that I take Allegra almost daily during peak season and a low dose (25mg) of benedryl at bedtime. Advil or Aleve for the general crappy feeling works well too. Steroids are find for 4-5 weeks, but not longer. That said, at even a low dose you might have headaches and have problems sleeping. Watch your caffiene intake during the steroid course so your head does not explode. Good luck!!
I am assuming it is the post-nasal drip that causes the constant sore throat? It feels more like chronic dry throat than anything else to be honest.