I Went Surfing Yesterday For The First Time In Years.

I went surfing yesterday for the first time in years. I'm 42. I noticed a tender lump below the bone/cartilage line in my solar plex area. You can trace the sternum cartilage left and right from the highest point on my chest down and to the right there is a noticeable protrusion and it is slightly sensitive to push on and when you tap it the dull thud is higher in pitch than the surrounding area. I don't remember ever feeling anything in that area other than a protruding muscle. I'm wondering if it's some kind of bone or cartilage growth? I noticed a small ball on the joint of my left thumb on the inside of the second most distal joint for many months now that gets tender to the touch and I've been monitoring it. It has the same unusual feel and sensitivity. What do you think doc?