What is wrong with my heel?

I stepped on an Electric screwdriver bit back in August. My foot was sore for two weeks but it healed. While the wound was open, I cleaned it twice a day every day and kept it bandage and covered with neosporin. I had a tet shot prior to the incident. My heel stopped hurting and it healed completely from the outside. About 3 weeks ago my heel started hurting on and off. Now it hurts every time I apply pressure on it. What is going on? Does anyone have any insight on the matter?