There is a strong possibility that this is asthma. It is a good sign that your chest x-ray is clear, but you should have spirometry done. This is a simple breathing test that measures how your lungs are working. It will show if there is obstruction in your airways that could be a sign of asthma. I suspect that the dizziness, headache and ears ringing constantly are unrelated to your chest and throat tightness.
http://ajrccm.atsjournals.org/cgi/content/abstract/200511-1736OCv1
It's very possible it could be connected to 9-11. I just heard on our news this week about many people getting respiratory illness after 9-11. There was even one death due to it. Do a search to see if anything is online about it (post 911 respiratory problems or something).
There is a very common disorder that resulted after 9/11. It is called Reactive Airways Dysfunction Syndrome, or RADS. You will be able to find some very good information on RADS on the internet. If you want any other information, feel free to email me and I will share with you what I know.