Sharp pain along the veins of my left arm. Cause?

Whenever I extend my left hand, I feel a sharp pains in a straight line on the inside of my arm, along the lines of my veins. It only happens when I straighten my arm and accentuates when I flex my fist back. The pain is like pressing on a fresh bruise and I also feel it when I press on the areas where my veins are located, from my wrist to my elbow. I do spend a lot of time at the computer and I often cut of circulation to it when I sleep. I am a 22 year old male by the way and I haven't practiced any kind of demanding physical activity that would damage ligaments.