Advanced Hygeine expert Kenneth Seaton warns of using hydrogen peroxide to flush out your sinuses. That could have something to do with your problem.
While the the formulation of one of his sinus rinses has hydrogen peroxide in it, it is in *very* small quantiites. You can get the solution from Clenzology.
Also, you can use a simple salt solution in warm water (about 101 deg F). The higher temperature will kill off most viruses and the salt keeps the water in balance with your body's salt levels.
The most effective way is to put your face in a bowl of the solution and blow bubbles. You can find some more information at http://www.coldfludefense.com/