Hi. I recently posted a thread of how I controlled my sinus problems through coconut oil and I couldn't help but notice that you said that your nasal passages with vitamin C. I too used the high dose vitamin C route and it did not work for me because mine is a completely different problem. I did read lots of books about vitamin C, actually, I am somewhat of a fanatic with it. Try reading Linus Pauling's book, How to Live Longer and Feel Better. Pauling is a world renowned nobel prize winning chemist, biochemist etc. He breaks down the Vitamin C to it's basic atoms and explains why vitamin C in high doses can cure many diseases. I, at one time did take high dose of vitamin C for my sinuses, and it worked for a bit, but it was the coconut oil from oil pulling that really saved my sinuses.
I suspect that your sinus problems are different than my sinus problems and perhaps that's why you reacted to vitamin C so favorably. There are some other websites you can check out that is more vitamin c specific, such as vitamincfoundation.org. The guys there are vitamin C fanatics. You may need to take vitamin C up to "bowel tolerance" meaning you should take it just enough, right before the water goes into your colon.
Perhaps that may help you, but of course, every disease is diagnosed differently for each person.