A 45-year-old female has presented to you in your GP clinic with sudden onset of pain in the left heel. She is complaining that the pain occurs mainly during the first steps after waking and is relived after walking around for several minutes. Despite this, she states that this pain worsens later in the day after prolonged periods of walking. You notice that she has an antalgic gait on examination as well as a positive windlass test. What is your diagnosis?