I have recently discovered a blister on my lower leg. It appeared literally overnight, four days ago. I discovered it after a night out and am told it looks like a brun mark even though I'm pretty sure it isn't. It was very swollen and quite itchy with a red outline. At first I burst it with a pin and drained the fluid, dressing it during the day and leaving it free at night. Today the blister is swollen and fluid filled again. I am not sure what this blister is, what caused it or what to do with it. Please help!