I have almost exactly same Rash/Corn/Wart on my middle finger for last couple of years. As you described "It starts as a raised bump that looks like a pimple. The pimple gets hard, flat and red. It then dries up into a white spot and then falls off or I remove it."
I used to wear a ring in this finger 6-7 yrs ago and the rash is inside on hand, where the ring used to be. I haven't discussed this with physician yet, but should I be concerned?