I've got severe pain in my left arm with tingling and numbness in my hand. i do a lot of lifting and repetitive motions at work.?

Cumulative trauma: Can result in a wrist synovitis resulting in carpal tunnel syndrome. Other nerve problems might occur, perhaps ulnar nerve at elbow. Consider disc problem at neck or even thoracic outlet syndrome. See a physiatrist, and get an answer. Perhaps an EMG might be useful.

Thoracic outlet synd: These are the symptoms of pressure against the nerves to the arm by tight muscles either above or below the collar bone. The diagnosis of the cause requires a physical exam by someone who knows how to diagnose thoracic outlet & pectoralis minor syndrome. There is no simple test to establish the diagnosis. X-rys and nerve tests can confirm the diagnosis but cannot do it without positive finding.