What Causes Extreme Pain In Left Hand Passing Towards Arms?

Hi I have been having very bad pain in my left hand that goes all the way up my arm. No pain meds have taken that pain away its hard to squeeze out a towel to was with that hand an even to hold something as light as a quart of milk to even a skillet. If I bump that hand even lightly the pain runs up that hand from my fingers up my arm what could cause something like this I ve had it for about 6 months or more. what can I do?