Just in case anyone is suffering from sinusitis, I thought I'd post this. I was a chronic sufferer and used to have nosebleeds and seasonal faryngitis. I was tired of antihestamines and antibiotics and nothing seemed to work. It was usually at its worst when I travelled from one climate to another which I needed to do for my job.
Then I started taking Vit C supplements on a daily basis. When I felt that it was really bad I upped it to 500mg from my daily 250g (recommended dosage). After a year my headaches and nosebleeds disappeared and 4 years later I'm still sinusitis free.
Since drinking Vit C supplements I also haven't had flu. The same principle applies, when everyone is sick around me, I up my dosage for a couple of days.