Chest Discomfort. Not Pain, Why?

I am a 53 year-old man, non-smoker, no history of heart or lung problems, i am 5'10, weigh 195. on December 25, i was outside in 25 degree weather briskly walking looking for my run away dog. i was wearing sweat pants, tee shirt and a sweat shirt, i was out for a about 15 minutes, i began to find it hard to breathe with a tightness in my chest. i came inside and sat down in the warm and was quickly able to breathe but i felt something in my chest like a tightness or discomfort --- not pain --- in my chest. i have felt this discomfort off and on for the past six days. it went away completely for a day and has returned today. have thought it to be digestive, but doesn't seem to be digestive related today. no pain or weakness in arms, just this anoying discomfort --- sort of what is left over after a sever gas pain (that you feel in the chest area) goes away. anybody have any ideas?