Upper left chest discomfort. Pressure.

Almost 45 days back I went for running in the morning ( in cold weather ). I ran for almost 2KM WHILE BREATHING WITH MOUTH. I was running out of breath still continued running and previously I haven't practiced running. At end It felt like some of my upper chest (left side) tissues got injured due to excessive pressure. Since then it's reoccurring and disappearing with sometimes  mucus (clear ) with coughing. And discomfort in upper most chest area in left side near middle. I got sick once cough and cold nearly one month ago . Since then the discomfort is more frequent. Consultanted with a  general physician , he told me not to worry and gave some meds which didn't work. * No family history with heart diseases * No family history with high blood pressure.