What Causes Severe Pain In The Forearm?

Hello i am 23 yrs of age and over weight for the last few days i have been having the most painful shock in my left hand. When this pain comes on it almost makes my whole hand weak and it makes me kind of jerk my arm back and weak it's werid iv never had this before. The pain is in my arm from below my elbow than goes to my hand.I dont have health insurance so I havn't got checked out. Do you know what might be going on?