Also, in future, the best thing to do about sunburn is as soon as you notice it happening, do whatever you can to cool your skin.
Sit in the shade, cover yourself in cold water. Anything.

The heat stays in your skin otherwise and continues to burn you. If you sort it out quickly you can stop it before it burns properly.
( Master Of Turnips. Only gays and morons believe in ghosts., Mon 25 May 2009, 17:12, archived)