I think you should have him tested for an immune deficiency disease by an Immunologist, NOT a family practice doctor. They don't know the right tests to do, usually. I have a very rare immune disease called CVID and for 21 years I was told 'nothing is wrong, your tests are normal' because some immune deficiencies/diseases CANNOT be detected by just checking the levels of immunoglobulin in the blood. He also may have a nasal polyp, this would cause facial pain and pressure and difficulty relieving sinus infection symptoms but it wouldn't cause him to get the flu - I get polyps all the time.
If you want more information I would go to www.primaryimmune.org, the website for the Immune Deficiency Foundation.
Good luck!
Hi,
How is your son? Blocked nasal passage may be caused by viral infections and structural problems such as nasal polyp. Your son may benefit from an evaluation of a specialist or ENT. If he had been infected with the flu three times in just three months, it would also help to strengthen his immune system. Take care and do keep us posted.