Have you thought about allergy testing? I've had chronic sinusitis for years and underwent allergy testing this winter. Found out that I am allergic to almost everything and taking allergy injection therapy has helped my headaches tremendously after only three months. I didn't have the outward symptoms of allergies (sneezing, runny nose, etc.) but did have severe headaches and tightness in the face. I would end up on antibiotics several times a year to treat the acute attacks.