What causes tingling in the whole left arm?

Brain or neck. Nerve pain as you describe frequently comes from the neck but can come from the brain as well. Lastly a nerve in the arm itself could be causing the symptoms. Best to see a neurologist to evaluate this.
Tingling. Many possibilities. The nerves going to the arm are sensing a problem either in the neck or shoulder (spinal condition, shoulder impingement, brachial plexus). Rarely brain or spinal cord conditions can produce similar presentation. The cause could vary from inflammatory process to compressive injury. Your physician, with a history and good exam, can narrow down the possibilities.