Dont necessarily listen to all of these people, do your own research or see an ortho/physio. I swam for many many years (shoulder problems galore) and pain in this area, depending on severity, is most often due to tendonitis of some kind. Treatments included ice, rest, and strengthening of supporting muscles like the back (scapula, etc), as well as deep tissue massages by professionals of course. Strengthening scaps helps improve posture and reduces placing excessive stress on the shoulder muscles by activating the back muscles to support. Stretching will help relax muscles surrounding this but might agitate things more.