I have a protruding breast bone... Help?

Okay so I've always been a skinny girl, and recently I've noticed that my xiphoid process (below the sternum) sticks out a lot and it makes me look super skinny.. I have a few questions: Is it because I'm skinny that it sticks out? Can I make it go away by gaining weight? And lately I've noticed that it kind of hurts when I breathe, I don't know if it's because of that, I have had pneumonia twice so it could be because of that, I just don't know if I should get some help for it.. I just want my bone to stop sticking out...