I have a very painful right foot. When I walk on the right side of the foot (the outside edge), it's ok. When I walk on the heel of it, it's ok. But when I walk normally, there's a pretty sharp pain in the meatier part in the middle of my sole, a few inches from heel. What is this? It feels like a strained muscle or something. It's not just regular sore feet from walking a lot. Any experience with this?