Its because of of frozen shoulder. Pain at night+stiffness (inability to move the arm upward and backward) , problem in daily routine activities. Diabetics are prone.
Next Steps
Go to a physiotherapist.. Ultrasonic therapy +IFT +Heating therapy +some strengthening as well as stretching exercises will be helpful for sure. This is the only option and without any side effect.
Health Tips
At home.. Hot water fomentation +pain killer gel +no side lying on same shoulder +no cold exposure +no jerks to the shoulder +no weight lifting+frequent full range shoulder movements .