What Causes Pain In Shoulders?

My grandmother has pain in her upper arms into her shoulders and becomes so extreme that even to touch her shoulder causes extreme pain. She is not able to sleep well or do daily activities. She is currently on pretezone (spelling?) and says that it helps but for only about two weeks and then has the same pain. Her family doctor told her he believes it is bursitis but I dissagree because, she doesnt do any streneous activity to cause the bursa to become inflammed or irriated and it is just not in her joints or even the immediate surronding areas, where the bursa are located. What do you think could be her possible diagnosis?