I have this as well. I finally found out that I have a severe grass allergy, so bad that medication alone didn't help. I began getting allergy shots about 6 months ago and it REALLY helped with this sensation.

It actually came back about 2 weeks ago (it's summer now). I feel terrible right now, and I can't stop blowing my nose. I am taking Allegra-D along with my shots (it has been helping in the past, but isn't right now for some reason).

I have had this weird gag sensation since I was in high school. I usually have a water bottle or something to snack on with me at all times because that is the only thing that seems to help at all (and even that doesn't make it go away, just helps a little).