What Causes Fluttering Pain In Back Radiating To Breast?

I am experiencing a slight , almost flutter pain under my right breast, seems to originate from the back...so slight that I could hardly call it pain...it just seems like something is not right...have had congestion and lots of coughing in last week....I am a 69 year old female....5 3 and weigh 200lbs...I am aware that I am greatly overweight...I do water exercises 3 times a week and walk some on the treadmill...was doing great and losing weight until I got sick.