A 34-yeаr-оld fаst fооd worker presents to your office for evаluation of bilateral heel pain. She notes that the pain is most intense when she first awakens, then eases up somewhat after awakening for a few minutes. By the end of the day, the pain returns to its full intensity. She has tried over the counter analgesics without success. She denies fever, chills, trauma, or injury to her feet. On physical examination, she has tenderness upon palpation of the heel. There is no erythema, deformities, or joint swelling. What is your most likely diagnosis?