Embishop,
I also experience the gag reflex. I'm not sure if yours is the same, but mine has to be a do with fluids only past a certain point towards the back of my mouth.
I am 6 weeks post rads, and it is much better now.
It was so bad that it was giving me an excuse to put off things that I needed to do, like the baking soda rinse and fluoride trays or just plain brushing my teeth.
But what I found to best overcome it, is to start any rinse, just in the front of my mouth, then keep repeating until I can go back far back enough to gargle.
I found this especially true with the baking soda /salt rinse.
As I worked my way back, with repeated rinses, it would take away the older mucus, which I assume was causing the gaging.
With brushing, I try to keep any toothpaste foam towards the front of my mouth, to spit out with littie effort. If I try to get every little bit out, even at the very back, it seems to cause the gag cycle. So it's a balance, I can live with a little toothpaste aftertaste, if it prevents the gagging.
I have always had this, even before the oral cancer, so I don't think that I will ever be totally over it, but it's way better, and manageable now.
My wife's coworker, who is a breast cancer survivor, gave me a very inspirational medal. It's a small Angel, that is imprinted with, "This too shall pass".
It's so true. It keeps me from dwelling on the current side effect, knowing things come and go. You will get through this, as unpleasant as it is. But we are all stronger then we realize, after the moment passes, and we are in sunny times.
Take care, be tough!