Don't know if it relates to your problem but I tore my left subscapularis tendon lifting which was misdiagnosed and unidentified for years before I had surgery done to fix it.
There are several of tendons that come together in the same general location, including the bicep, pectoralis and subscapsularis tendons, so it could be something other than you think. Here's an article about the subscapsularis tendon tear -- Subscapularis Tendon Tears | ShoulderDoc -- and another about bicep tears --http://orthoinfo.aaos.org/topic.cfm?topic=a00031.
Whatever the cause of your problem, I hope it's not serious. Good luck!