Woke up in the middle of the night while sleeping on right shoulder and felt a "pop". now the back of my shoulder has been hhurting for a week?

Shoulder injury: Shoulder pain often indicates rotator cuff problems. Often it's a dull aching pain worsened with activity. Lifting the arm overhead commonly produces pain (lifting things overhead). Sleeping on the bad shoulder at night is a common cause of pain with rotator cuff problems, many who have a history of previous (ie sports) injury. Pain, even in young patients, may indicate arthritis. See your doctor.