I Have A Small Hard Lump Between Two Ribs Where

I have a small hard lump between two ribs where they join the sternum. It’s about the size of a marble and has become progressively more painful over the last week. Pain is a sharp, stabbing pain in the lump when I move my arms or breath deeply. I’ve been doing a lot of lifting and crawling around inside an airplane in odd body positions while doing maintenance during the time the lump developed.