I have pain on my left side by my my left shoulder and under my armpit, it has been coming and going for weeks now. I am 25, a non smoker, weigh aboutt 250. I am 5 ft 5 I went to the er two months ago, nothing was wrong with my chest xrays and ecg. They thought it may be a strained muscle, but could it still be. It freaks me out and I start sort of hyperventilating.