Hi Matt -
Me too, and right where you are describing, although I had twin drain holes with one on each side. I can't remember if the doctor called it dislocated cartilage or inflamed or what he called it, but IT HURT BADLY for several months -- same location as you are describing. I think it's the bottom rib, where it attaches to the sternum. It did gradually get better, but laughing was one of the things that was agonizingly painful for quite a long while. Lots of things would make the pain ZING; even sitting for long periods of time, like if we would go out to dinner with friends, would make it hurt.
I did find some other people here on VR.COM, who experienced similar cartilage problems so maybe they'll see your thread and post.
My chiropractor recommended a rib belt when I saw him a few months after surgery -- he suggested I wear it for a month -- but I declined. I'm not sure that would be a good idea for a heart patient still recovering to be wrapped up tightly like that.
And, not to scare you, because it may not be as bad for you, but here I am, well over 3 years out, and it still hurts sometimes but nothing like the pretty awful pain I had early on.
I think good posture might be your best friend for the time being. Hang in there. Who would think a rib or some cartilage could cause so much pain?!