Certainly not a fungus, or a reaction to Lamisil.
This sounds like an eczematous rash, quite possibly a contact dermatitis to the dye in the shoes, as the podiatrist suggested and quite properly treated you for.
My guess about the recurrence and worsening is that you are experiencing a rebound now that the cosrtiosne has been discontinued.
I would call back the podiatrist, or consult a dermatologist, about resuming cortisone by mouth for another 5-10 days.
Once the skin heals, allergy patch testing, which dermatologists do, may be useful to pinpint which chemicals you may be allergic to and want to avoid in the future.
Good luck.
Dr. Rockoff