I Have Itching On My Left Hand On The Thumb

I have itching on my left hand on the thumb that has progressed up to the elbow area. Then it goes into a burning sensation from elbow to shoulder and across my shoulder to the neck . It comes and goes and occurs mostly when i'm sitting or driving the car. This started out a few years ago as just a constant itch on my left thumb. It is only on my left side. Whats going on?