I run a lot and strike with my forefoot. Sometimes I have sharp pain going from the outside of my ankle behind?

the bony bit. It feels sort of like when you pinch a nerve or strain a tendon. It goes from my outside ankle up the side of my calf. When I get this pain my ankle feels really unstable and weak too. Any way I was wondering if any sports therapist or doctors could tell my what may be causing my pain and if it may be my shoes or stride?