Thank you for your query at DoctorSpring.com
I had gone through your reports that were attached.
However I didn't find a sleep study or echo study report.
The lung function test and ct scans rule out a lung problem so as to cause this much of breathing difficulty.
Spirometry though suggestive of restriction, is probably due to a weight gain. The diffusion capacity is normal and ct scans also are normal. Absolutely there is no evidence of asthma, smoking related diseases, interstitial lung diseases or pulmonary embolism.

Suggest weight reduction. Echo to rule out pulmonary hypertension ( though ct does not mention it). Sleep apnea can also produce a fatiguability and cause breathlessness, so can hypothyroidism. Suggest to rule out both.
Hope that helped
Regards

Dr. Jacob George P
MD, IDCCM, FCCP