I have been having some deep breathing chest pain whenever my breathing gets too intense, such as running after 10 tennis balls in a tennis match, or playing basketball, or running up a hill. I have not been exercising much this year, because I've had a thyroid problem, when it feels like I have some energy, I try running, then often have to quit because of the thyroid issues. So I haven't been exercising regularly. Could it just be that I'm expanding my chest wall more than usual and that hurts? It also hurts when I press on my chest when this happens, it Feels like a lot of pressure. It doesn't seem to affect my breathing except it hurts. I just want some verification that it's not something more serious. Cause I want to start running again 3 times a week, without having to worry about it. Thanks 39 years old, thyroid problems, no other issues. Mr.E.