Almost a month ago I was walking around outside barefoot. I felt a sharp feeling in my foot, but believed it was just a rock, I looked at my foot and nothing was in it, and no blood. It started turning into a bump, and now there is a dark spot there that resembles a blood blister , still with a bump slightly larger then a pea. When I even touch it, or step on it wrong I have a sharp pain in it. What could it be?