What Causes Pain In Sternum While Coughing?

I spent 4 days in the hospital with pneumonia. I was discharged two days ago. When I cough it is very painful in my chase around the sternum. I am not coughing much now but when I do the pain is about a 9 or 10. I also have developed a muscle bulge in my left calf. I am taking hydrocodone to get the pain down. It feels like the sternum is broken.