Itching Under Foot, Become A Callus

Hi doctor, I ve got this never ending itch under my right foot . It is located direct center of the foot, just below the pad . It comes and goes but when it s there, it feels as if it is deeply rooted under the skin. I ve itched it so much, it has now become a calloused mound, yet the relief i get from itching it is almost indescribable. I often take sharp objects to better penetrate the source of the itch. I am 21 years old, in good shape, and stay active. There are no visible signs or symptoms on the skin that would point to a diagnosis.