Just thought I would post this as I suffered for a few years after contracting a flu and sinus problems. Surgery didn't work initally, and I was about to increase my life insurance as no one could figure this out. I checked out lactose intollerance and none of the sypmtoms had any connection. Then I googled "is lactose intollerance and a dairy alergy the same thing" and realized DAIRY ALLERGY WAS THE BIG KEY. Was eating a lot of greek yogurt trying to get healthy eating the right foods. Cut out a lot of the eggs that I was eating as well. I was a social out cast and was really having trouble with work. My friends knew how sick I was and doctors would slowly pick away at tests. My advise to anyone who has the cough is to get a CT scan of your sinus's and cut out the diary!