I have an unexplained bruise on the sole of my foot, directly under the arch. It is about 10mm in size. I have not hurt my foot at any time. My foot does get painful if I have been walking or standing for any length of time, though th pain is mainly around the ball of my foot, at the side nearest the arch, but I definitely have not injured it. I would be most grateful for any help or advice that anyone could give me.