Common reasons could be
Cold and cough which may be seasonal or allergic
Or it can be simple acidity related
Next Steps
try to show your family physician to rule out common associated causes or if he feels he can suggest u some other cause and treatment also.
if he recommends go for relevant investigations including PFT .
Health Tips
as u mentioned u get benefited with breathing exercises , so let's continue with pranayama and yoga to strengthen lung function as well body and mind health.