It certainly sounds like something is going on in the shoulder! I would recommend that you go see your doctor
about this, if you have not done so already, as they will be able to help guide you through the possible diagnoses and treatments.
A rotator cuff injury
is one of the most likely possibilities. As you may know, the 'rotator cuff' is the name for the group of muscles that surround the should joint and stabilize it when you move your arm. Rotator cuff injuries are most common in those who use their arms actively, such as in sports or weightlifting, or repetitive jobs involving heavy lifting. However, they can happen in anyone even with relatively minor physical stress in the right circumstance. Rotator cuff tendonitis is the most common injury, and this usually responds to anti inflammatory medications, shoulder exercises, and physical therapy. If the injury is more severe, resulting in a tear of one of the rotator cuff tendons, then referral to an orthopedic doctor and shoulder surgery
is sometimes needed instead.
Your doctor will be able to examine the should and determine whether you have a rotator cuff problem, or whether your shoulder symptoms are due to another problem all together.