What can cause arm pain (left)? feels like it's hard to make some movements.i sometimes have to take my other arm to lift my arm because it hurts

Shoulder likely: Shoulder problems such as rotator cuff injury, arthritis, and subacromial bursitis can make use of the arm painful. Heat, non steroidal anti-inflammatory medications, and range of motion exercises, and rotator cuff strengthening can at times help. If persistent, see a hand or orthopedic surgeon who specializes in problems of the hand to shoulder.