You should try a decongestant, or allergy meds that contain a decongestant. Like Claritin-D.

Good luck!

My allergies did the same to me for a while. I had post-nasal drip like crazy which resulted in a very sore throat. I ended up with strep-throat (though I believe the 2 are unrelated as strep is bacteria), but now I'm on Allegra-D and it works well for me.