I had the exact same problem.  Casual walking, fine.  Fast walking, hiking, or jogging/running, painful.  I alleviated a lot of my pain by doing three things:  (1) do a long warm up and then stretching, (2) landing mid-foot when running, and (3) stretching after cool down.  The change in running form made a huge difference.  I was gettiing very discouraged and demoralized with the amount of pain I was feeling when I first started C25K.  I started reading about running form and watching youtube videos.  Then I adjusted my form and slowly, the pain went away.  Good luck!