So I have this rash on my legs that hurts really bad and the doctor doesn't really have any idea as to what it?

At first I thought they were ingrown hairs from not shaving enough. ( I was w/o razors for about a week) but they have become very hard and hot with a sore in the center. I saw a couple in its early stages and they appeared to start as blisters. Now they are the size in diameter of about a golf ball and when I woke up this morning my knee joint on my left side and possible the leg bones themselves hurt severly. I had a few blood tests yesterday and they all came back within normal ranges. Anyone with similar or any ideas?