My symptoms and story are extremely similar to yours. All my test are “normal”and I’ve been diagnosed with asthma (worsened by anxiety). Treatment so far has been very successful, yet I still produce thick, sticky “mystery” phlegm on most days without cough. My pulmonologist (one of the best in Atlanta) has scheduled me for my first CT scan next week. It’s been explained to me that a CT scan is helpful in diagnosing more severe forms of asthma. I’m actually doing MUCH better now and thought about canceling the scan, but for peace of mind I’m committed to it (if something else is in play, I want to know about it). You may want to ask for one ... it can’t hurt and I wouldn’t worry about radiation from this lone scan.