Have you had your thyroid checked for a Goiter...I had this and couldn't swallow...
Gagging can be due to many things, it is a natural way to stop you choking, people may find they gag for no reason.
Try these tips to help:
Breathe in slowly through your nose. Take deep breaths, which will help to calm you.
If you know there are places you are likely to suffer, try using a nasal decongestant before you go to them.
Try using an anaesthetic throat spray, such as Vicks Ultra Chloraseptic throat spray.
Try using hypnosis. A lot of the time, gag reflex problems are more in your mind than anywhere else. Listening to a good hypnosis program can make all the difference and can make your life bearable again
Hope some of this helps Cupcake!