I have a small lump just above my ankle on my left foot on the outside under the skin. If I bend over it feels as if a string is pulling it tight and the pain only at a certain angle is almost unbearable. There is no sign of bruise or bite and it gets much worse after I have been walking or try walking up stairs. It feels like it is radiating up my leg in to my calf and knee area and up into my thigh area on the outside only and all under the skin. Tender to the touch where the lump is at my ankle area. What could possibly be causing this?