Left arm pain with shortness of breath and left shoulder pain can be due to a wide range of problems. Since you listed "cancer" as one of your current medications, I wonder if you're trying to say that you currently have cancer, or that you're worried that these symptoms could be due to cancer. It's important to ask your doctor about these possibilities: muscle strain, bursitis, rib strain, pleurisy, pneumonia, and less likely but possible: heart problems.