Advice for terrible sunburn?

I went to the lake today and, of course, got burnt by the sun. The back of my legs is the worst of it. It hurts just to walk across the room. The sun left its tattoo on me everywhere, though. (Including my butt.) This makes it hard to be even slightly comfortable. Any advice?
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Thank you so much for the answers, guys. I've been drinking a ton of water and Gatorade and that pretty much did the trick. :) The aloe lotion worked well, too. Guess who's doubling the amount of sunscreen next time?
Advice for terrible sunburn?
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