Not Sure How To Describe Exactly What I Am Feeling

Not sure how to describe exactly what I am feeling on occasion in reference to my respiration (i.e. not sure if it is a lung or heart symptom). But here goes, I don't seem to breathe as easy anymore (43 y/o male, hispanic, nonsmoker, regular exercise, military) within the last few months I have noticed that the air seems to sort of respirate out of my lungs with a slight burning sensation around the middle of my chest.