Share 'Left hand pain'

I've been playing for a few years now, completely self taught and I've always had a problem with pain in my left hand.  It's in the thick fleshy area right below the thumb.  I can only describe it as the burn you feel from exercising a muscle.  It doesn't cramp up, it just hurts and I eventually have to quit playing and rest it.  I can't make it through certain songs that are longer and require c…