Re: Allergies or GERD...?
I think it could be a side effect of your medication.
I use two medications myself for Asthma and both cause me dryness at the back of my throat at times even though I use a Volumatic-Device. What you describe is more likely irritation than itching.
Like jane said you can try a gargle/mouthwash. I find warm milk with some honey quite soothing. If it continues let your Dr know as it could be a reaction to the medication .
All the best,