Stiff, sore pain on the outer side of my leg just above my ankle.?

When I go for walks, right above my ankle on the outer part of my leg, the muscle seems to really stiffen up and get sore. If I curl my foot inward (toward my other foot), I can feel it stretching the muscle or tendon or whatever it is. Is there a stretch I can do before I walk or something to get rid of this?