Poor spirometer readings

[fatigued123]

A couple of months ago I had a bout with a cold/flu in which I wasn't feeling better after the regular cold/flu symptoms abated.  Was feeling so poorly that I went to the doctor for the first time in years.  He gave me a spirometer test, found that my breathing function was about 1/2 where it should be, diagnosed an "asthmatic episode" and sent me home with an inhaler.  Weeks later I was still feeling exceptionally fatigued, with chest tightness and a mild cough that wouldn't quit. When I returned to the doctor, a second spirometer reading showed insigficant improvement, so I was referred to an asthma/allergy specialist.  The specialist gave me a 5 day prednisone trial which failed to improve my breathing (although I did have a fantastic energy surge which unfortunately was just a side effect).  Now he's suggesting it could be either a) post nasal drip complications, for which he's prescribed patanase; b) GERD, for which he's given me protonix; or c) vocal chord dysfunction, for which he's recommended breathing exercises.  After 3.5 days I'm feeling even worse, with headaches (possibly a protonix side effect) and intermittent anxiety, which I'm wondering whether it may be related to poor breathing, or my heightened awareness of my breathing.  So:
Are the low spirometer/peak flow readings something to be concerned about, or is it possible that I've had them all along?  
Am I correct in linking the low readings/low breathing rate to my feelings of chest tightness, persistent low level cough, fatigue and general crumminess?  (I also have IBS, which is also a factor in the fatigue, crumminess realm; it may be exacerbated by the fact that my cold, flu, cough, breathing problems have hampered my exercise routine, which helps control the IBS),
Is it really possible that the minor post nasal drip I have could be causing a breathing obstruction?
If reflux is the culprit, wouldn't/shouldn't I be feeling some of the other symptoms?
Are there other causes of breathing obstruction, other than those mentioned?

Any light on these issues would be appreciated.