What Causes Throbbing Pain And Soreness On Sole Of Foot And Ankle?

I have pain in the bottom of my foot at the rear of the ball of my foot. The pain is in the rear center of the ball of my foot, I do not recall stepping on something that caused pain in that spot or any injury or blow to that part of foot which may have caused the pain. I have tried several different pairs of shoes with variable padding to see if that alleviates the pain but that has not helped. When I elevate my foot I can feel it throbbing and it is sore to the touch. It does not appear to be swollen when compared to my other foot.