Why do i feel that my vein from my left arm hurt, what does it mean?

Is it the vein?: It could be the vein, or it could be the structures surrounding the vein, like tendon or muscle. Is the skin over the vein red, warm, painful? If so, we think of superficial thrombophlebitis or just phlebitis. It can happen with trauma like needle sticks or after putting in an iv.

Arm vein pain: You are not too descriptive of what vein location or whether your arm is swollen. Local inflammation is constant, warm and painful. Musculoskeletal structures near veins can produce intermittent pin prick sensations with motion. Blockage of the vein entering the shoulder can cause swelling and pain due to repetitive effort like pitching (padget-schroeder syndrome) and is serious. See your doctor.