I've been having this recurring discomfort in the upper left side of my chest for about 45 days now. It all started after I went for a run, breathing through my mouth in the cold weather, and I felt like I'd somehow injured the tissues on that side of my chest from the pressure. The discomfort seems to come and go, sometimes with clear mucus when I cough. I did have a bout of cough and cold about a month ago, and since then, the discomfort seems to be happening more often. I've already seen a general physician who said not to worry and gave me some meds, but they haven't really helped. There's no history of heart issues or high blood pressure in my family. What do you think could be going on?