If you are protracted or internally rotated at your glenohumeral joint you could be suffering a shoulder impingement and/or subacromial bursitis. Where exactly is the pain felt and does it occur during any other exercises (ie. during GH abduction, extension, flexion, external or internal rotation)? Like organicshadow had said your posture has a lot to do with this. Perform this test, this is for shoulder impingement. Place the hand of the affected shoulder across your body and on the unaffected shoulder. Keep the palm firmly in contact with your shoulder then raise your elbow to your nose without flexing your neck to assist in contact. If pain is experienced at any point, do not push through it, or the test can not be completed it is a pretty good indication of shoulder impingement and you may want to seek the help of a professional. the forum wont let me pos the picture yet but if you google: Elbow raise shoulder impingement test, the first picture is a good representation.