I had sinusitis for years and had all your symptoms except neck pain. If you do have a sinus infection it will show up on a cat scan. An additional clue to a sinus infection is that sometimes everything smells like sewer gas, especially when you lower your head...also, your teeth on the infected side hurt. Strong antibiotics over a long period of time are necessary to treat this. It sometimes takes over 6 months of antibiotics to clear it up. Good luck.