I'm Having Trouble Moving My Right Arm. When I Walk,

I'm having trouble moving my right arm. When I walk, the left arm moves normally, the right one just lays there. I can consciously move it, but I've noticed lately that when trying to use both hands in concert to do a task, like shampooing, the right hand is very slow and does not sustain as long as the left hand. I had tennis elbow last year and received treatment and now I have this. What could it be?