I recently started going to the gym. I am over weight and have decided that I want to make a change for the better and get healthy. I am currently doing cardio when I workout, usually just fast paced walking on the treadmill for 1 hour. I have done this about 5 days so far, but today after my workout I had a bad pain on the left side of my chest. It seemed to be right under my left breast, near where my heart is. Is this something that is normal, considering I have led the last few years of my life being fairly unactive?? Should I be concerned about this??