Suggest Treatment For Irritable Black Spots On The Heel

i have had these black spots on my heel, i have hard skin because i have a thyroid problem, my heels cracked originally and i did put a good cream on, however these black spots which are very irrritable, almost like they are eating away at my heel, never go away, they go yellow around the head with a yellowish hard puss, then they go hard and peel of like plaster, then i seem to go through the cycle again, i have had this problem now for about 6 months. What is it?