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

C5 radiculopathy. Disc herniation atc4-5take out your deltoida complete list also includes stroke get it looked at.
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.