my son has a medium bump on the heel / sole of his foot. It looks like it's filled with pus. It began very small a few weeks ago and felt a little hard when touched. We thought it was the beginning of a planter wart and bought pads. He showed it to me tonight and its now medium large and the pus filled. It sort of looks like there is a tiny black thing inside, and we picked at the top with a pin to see if it would release but nothing would. We covered with Neosporin and bandaid to moniter. Could this just be an infection and something like a tiny sliver is inside and the body will expel or could this be something severe to get checked out?