Do you think this has come up after you consumed some oral tablet (for any reason)? What I can suggest is to stop scrubbing because it will only aggravate your pigmentation. And go visit a dermatologist allopathic near you . An examination of the oral cavity mucosa and other body parts is needed to rule out other pigmentation disorders. And like I said, try to figure out if you had any medication at all before this came up.. or if  this gets aggravated on ingesting any oral tablets.