also bear in mind that cycling is a non-loadbearing activity that gives you a powerful respiratory system and strong muscles with a limited range of motion. Running requires different muscles as well as impact-absorbing ability, and a much greater range of motion in hips, knees & ankles. Because your respiratory system is already developed you are able to push beyond what your musculature system can handle. I think you are on the right track with short, frequent runs at whatever speed is comfortable (i.e. don't focus on getting faster or going further. rather try to run more often, but don't try run through the pain). In addition: As suggested by others, get your footwear checked out by a reputable shoe-guy;get off the hard surfaces and onto grass, trails, outside lanes of athletic track;do some supplementary exercises that strengthen your running & balance muscles & their range of motion;stretch regularly & use a foam roller.hope this helps.
