I read your post very well, I was just saying in my experience it has always been a mucus problem. The mucus expands the adnoids and the passages go closed. Medically they have a HUGE LONG WORD to explain it and call it an over active nose, but when your fasting, it all relaxes and we can breathe freely.
If it has zero to do with mucus, then I have no clue what your problem is, most likely a "specialist" would have a big huge name for it and prescribe a drug.