My Left Forearm Sometimes Gets Stabbing Or Cramping Pain But

My left forearm sometimes gets stabbing or cramping pain but I can't physically feel a cramp. The pain feels deep, not close to the skin. The pain will last 5 seconds to a minute, usually closer to 5 seconds and then stop for a few seconds and start again. The pain will come and go 2 to 20 times, usually closer to 20, and then be gone for an hour or a day. It's not associated with exercise. It has woke me up at night a couple times but is generally felt during the day. It's not specific to morning or afternoon. I can still use my arm (have high pain tolerance) and it doesn't seem to hurt more while using it or trying to relax it. The pain sometimes stays in a given spot and sometimes moves several inches down my arm. The pain is always on the top of my left forearm and no where else. I'm 50+ years old, 5' 11", 205 lbs, have a decent amount of muscle (curl over 100 lbs, bench about 200 lbs and leg press over 600 lbs).