Wierd feeling in center of chest. Issue.

Hi, since past 3 months I am noticing that I have a very wierd feeling in my center and left side of chest. 2 months ago while doing a workout I had a sudden chest pulpitation but no pain. At that time I have consulted cardiologist and he asked me to go for few blood test and stress test. All my reports were absolutely normal and doctor asked me to join gym and don't take stress.. Since then I have that feeling everyday. While coughing I can feel there is something in my center and left side of the chest ...but it goes away... I can do my regular activities without any issues.. I can run, do my moderate workout with no issues but that wierd feeling in center of my chest doesn't go...I just wanted to know what should I do to resolve this unexplained issue.