I am recovering from frozen shoulder also. One of the things they did to test me at the Orthopedics office was to have me straighten my arms in front of myself at waist height, straight out. Then try to flip my palms over and under. I couldn't which seemed to help prove it was frozen shoulder, along with not being able to put my hands and arms behind my back, raise them up over my head and also to make chicken wings and try to flap my arms. I went through a year of pt which didn't solve the issue, but am doing slightly better now with many therapy exercises later. I wish you the best and hope that your doctor can help you solve the issue on if it's frozen or rotator cuff.