High O2 Saturation Level but Cannot Breathe

I got a microplasm IGM last November (I quit smoking in February 2010) and then I got C-diff from antibiotics and then pancolitis (I was told many people get colitis after quitting smoking), and was hospitalized for one month.  I had a stress test and that came out fine, yet I still could not breathe, so next I had pulmonary function tests.  I have mild COPD.  Spirometry at BTPS show FEV1 and FEV1/FVC are mildly decreased, FVC is normal (not a significant response to inhaled bronchodilator).  Small airways flow rate reduced (decreased FEF 25-75). Maximum minute ventilation is normal.  TLC is moderately decreased.  FRC is normal, RV is decreased.  RV/TLC ratio is decreased.  Single breath diffusion capacity is normal.  Combined obstructive and restrictive flow volume loop contours.  Normal alveolar-arterial gradient 7.42/47/84 room air.  My heart rate only significantly increases randomly.  I feel like I am suffocating or breathing in polluted air.  Before I got my microplasm, I could breathe fine.  Now, I have times when even walking 10 yards suffocates me, but I'm not huffing and puffing (SOB).  My doctors are stumped.  I would appreciate any help.  I also had a sleep apnea test which came out normal.  Thank you.