What Causes Pain In Elbow After Taking Brachial Plexus Nerve Block?

I had a brachial plexus nerve block 3 weeks ago. During the procedure I had an immediate stinging pain radiating to my elbow and to my thumb. I am still having pain along this pathway. I had same nerve block pre-op 3 months ago in other arm and did not have any of these sx. Was the nerve hit by the needle injection? If so, how long will sx last?