Hello, Based on your information, I would say that this might be tendonitis of the rotator cuff muscles which moves the arm. In other words is overuse of muscle that participates in weight lifting activities. Maybe you are doing heavy weights or very intensive exercises. I would like to have more information regarding which movement causes you more pain. Is it painful when you lift the arm in front on the side or backward? It might be also biceps tendonitis if the pain is in the front part of the shoulder and pain is worse when you bend the arm against resistance. My initial treatment would be rest from weight lifting activities and switch to other sports such as running for a while. Take some Ibuprofen. You can use also ultrasound device on physical therapy centers. If after this treatment you are not better I would order a shoulder MRI to see deeper the problem. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Edvin Selmani