On My Left Arm Right Below My Elbow A Small

On my left arm right below my elbow a small area became very sensitive to touch. It was not bruised, it showed no visual problems. However, it felt like it was a bruised area. It stayed this way for about a week. Then the same thing happened on the same arm right above the elbow... and now it seems to have moved to the top of the arm, near the edge of the arm pit. Still no visual sign of injury. I have no recollection of hitting it or hurting it in any way. All areas are still sensitive, however are improving except for the area that started hurting today. What could this be?