The shoulders are represented in this photo as cups stacked on top of plates. The largest plate on the bottom is meant to be the pelvis. Notice when the pelvis on the bottom of the stack of plates is out of place it translates all the way up the spine to the shoulders. When the pelvis is out of place, the spine bones, ribs, and shoulders cannot fit as they are supposed to. This is why I have learned to teach people to treat the pelvis and spine before treating the shoulder with physical therapy treatments. For many years, I treated the shoulder without success on patients but when I changed to focus on the treatment of the pelvis the shoulder pain improved.
Here are three simple stretching exercises that can help with pain in the shoulder. Pay close attention to other joints and see if that pain improves as well.
The best way to start treating the shoulder is to doe the "twister series" specialized stretches to treat the pubic bone, pelvis, spine and ribs