I'm training for a long distance charity walk and started with a 20 mile walk four days ago. I ached the next day, but mostly dissipated. Yesterday and today, however, some mild swelling has developed on the front of my leg just above the foot making it painful to bend my foot up or down. There's no discolouration, but the pain builds up after walking for a few minutes, so I've been using a stick (but not for any more training walks, mind you). Can you tell me what this might be?