Plantar Fascia? If it's the same i think it is, then it takes fucking ages to get rid of. I've had it in both feet and at times i could barely walk.
Had it for a year. At the end my body gave up trying to heal it, so i had to get some electro chock treatment, and it helped a lot.
Not sure if it's called electro chock treatment though Damn it did hurt, felt like someone was drilling inside your heel.