It hurts to stretched out my arm. Like burning or stinging in my left bicep on the inside of my arm. Like something is pulling my skin. Doesn't hurt unless I stretch or touch it. Started yesterday and woke up today with the lower part of the same arm hurting the same way. Hurts when I bend my wrist but the wrist itself doesn't hurt. Now there is a bruise on my bicep trailing down just like the pain. No injury at all. No exercise. What causes this?