Hello, You had a chest concussion injury. Now you are experiencing pain and soreness in the sternum. Your symptoms are indicative that the cartilage that connects your ribs to your sternum has becomes inflamed. This is symptom of costochondritis. Other medical conditions that cause similar symptoms are angina, heart disease, lung issues, OA, etc. Get CT, MRI, X-ray to detect the pathology so that treatment can be started at the earliest. Get clinically examined by a GP. You can take NSAIDS, Combiflam or Naproxen, one stat when needed. Your treating physician will give you conservative treatment and may refer you to a physiotherapist for stretch exercises and transcutaneous electrical nerve stimulation (TENS) if needed. Do not neglect, get treated at the earliest. Neglect may worsen the symptoms. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician