For the first time this week, I felt a bit of pain at times while paddling. It only occurs on the left side of my rib cage, a few inches below the bottom of the sternum at the end of the ribs. It is a bit of a sudden shooting pain, like a rib was trying to poke back into me, which goes away fairly quickly after readjusting my torso a little bit. Paddling more from my chest seems to cause it to happen less. Any ideas?