Can constant post nasal drip cause frequent gagging? i have had freq. pnd & have started gagging frequently the past week or two

Yes but: I would also need to rule out a sinus infection when the problem is that severe. See doctor.

Yes: Chronic rhinitis presents with a variety of symptoms including nasal congestion, running, itching (eyes and nose), and post-nasal drip that can be severe. Some patients describe it as "drowning in snot." Triggers can be allergic (animal dander, pollen, dust mites) or non-allergic (strong scents/odors, cleaning products, weather changes). See an Allergist to get this under better control.