Since both rounds of antibiotics did not help, you may have to have a punch biopsy of it. They will check to see if it is a fungal infection and if so, they will give anti-fungals to treat it.
It is possible that it is just a regular infection and they have not found the right antibiotic to treat it yet, but you need to let them know the second one did not work.
Best of luck and let us know how it goes. In the mean time, keep the area clean and covered if it is in an area rubbing against sock, pantyhose or shoe.
Lindaru