What Causes Sharp Pain On The Ankle?

I do running and totally have no feeling of any discomfort or pain on my legs, but i just discovered about 3 inches above my left ankle, on my calve bone area , i discovered there was a sharp pain when i rub on it, and there is a depression when i pressed on it, the size of a thumb. the tender stretches an inch across the bone part. Is it a hairline crack or stress fracture or could it be any kind of infection?