hi, thank-you for providing the brief history of you. as you mentioned you had lumpectomy done on the left side and also undergone radiation two years ago the cause of the process needs little explanation from your side to assist further. as you know, that the muscles of the respiratory system needs a good strength for which you can perform regular deep breathing and costal breathing exercises which will overall improve the capacity of lungs, improve the strength in the respiratory muscles and improve the oxygen blood carrying capacity. which will add on to improve the metabolic function and also important for the immune system. also you can take an expert visit and get checked once in person as hands on examination provides good diagnosis. With the grace of God I wish you a good health. Regards Jay Indravadan Patel