What Causes Pain Behind Left Shoulder And Under Left Clavicle?

I'm a 17 year old female, and I'm in relatively good shape, but for the past few months when I go running, I've been getting a pain behind my left shoulder blade and under/around my left clavicle. It feels similar to abdominal cramps that I've gotten while running, but it's worse (more like a 7 on a scale of 1-10 rather than maybe a 4) to the point where I have to stop. Also, sometimes the pain spreads to my chest. I have exercise enduced asthma, and I'm wondering if this is related or something else. Is it something I need to worry about?