protruding sternum with discomfort after heart surgery

I had open heart surgery for an aortic valve replacement 7 months ago. It seems like my sternum is growing and is protruding. My lower chest is very sensitive to the touch. My chest get irritated when I exercise and bothers me quite a bit for a few days then subsides some. It hurts sometimes when I cross my arms over my chest. It hurts sometimes when I bend forward. What's the sternum made of, and can it grow? Can what seeing be scar tissue from the large incision made in my chest for the heart surgery?
Robert

I had valve surgery 15 years ago and have the same problem. Did you ever get any answers?