I noticed sometimes after I stretch my arms (upwards) I immediately get a stinging pain above my right breast, slightly below my collar bone. Um, to kind of pinpoint it, see here http://tinypic.com/view.php?pic=2e19kef&s=5 (black circle)

It lasts a few seconds but it's quite painful, like something is stinging the pectoral muscle from the inside. What could be wrong?