I wish I could give you a definite answer but I can't... I had that same thing a few years ago. I kept smelling this weird smell. I turned my apartment upside down and cleaned everything.. But then when other people came over no one else smelled it and I figured it had to be in my sinuses or something. Eventually it went away on it's own after a few weeks and I never did figure it out. The only thing I can think of to try first would be to buy some of that nasal saline spray and clean out your sinuses several times a day to see if maybe it's something in your nasal cavities causing the smell.