The one time I got a burn that looked like a handprint

I woke up during the middle of the night Sunday because my leg was really hot and uncomfortable. It seemed like a bad sunburn right behind my knee. I ignored it and went back to sleep.

Work on Monday was normal. I remember showing a co-worker my leg and saying how I didn't understand how it could be so burned in JUST THAT ONE AREA.

Monday night, I noticed a few blisters forming. Put some after-sun lotion on it, still thinking it was a sunburn. Went to dinner. Noticed TONS of blisters all over the back of my knee -- not the clear kind you get from new shoes. These were some clear, some yellowish.

Made a genius move and went and ran 5 miles. I didn't really notice the pain/anything while running. But, man, it hurt afterwards.

Tuesday morning, woke up. It is still SUPER red. And covered in blisters that make me want to cry every time I bend my leg. Needless to say, I didn't make it to work. David gave me benadryl and I think I slept for 6 or 7 hours? I don't know really.

Wednesday, it's better. Still really bad. All the girls at my work have NO idea what it is.
So I go see one of my doctors on Thursday. She says it looks like a chemical burn. What throws everyone off is that it looks almost like a handprint with fingermarks.
Seriously, I'm still confused. I can't think of anywhere that I sat, or things I might have touched that would cause this.
I'm on a course of steroids (oh, roid rage, you are a pain) and a crazy antibiotic but it is still going away so slowly.

Today, Monday, makes it a week since I noticed anything. And I just barely got all the scabs from blisters to start coming off.

Anyone else have a weird, creepy handprint on the back of their legs that burns?
I'm thinking of starting a club. Victims only, though I should probably stop playing that role. I can walk, I'm not dead..... Yet.

(Sorry for the gross pictures. The white-ish one is from Wednesday. The other one from Saturday.)