On Sunday I sustained an injury to area just left of my sternum, above my left breast and below my collar bone - I was hit with the back of a hand. It hurt immensely at first but I'm 110lbs and 5'7" so I figured it was just my lack of pain tolerance. However now I am experiencing intensely sharp pains in that area and also in my left shoulder blade - almost feels as if it's underneath/right next to my spine. I experience these pains every time I breathe, move my left arm or put any type of pressure on my left arm. I've also began to notice them when trying to blow my nose or sneeze. I'm wondering if the tissues is just severely bruised or if I may be suffering from a cracked or stuck rib - any input is appreciated.