What shall i do about this sunburn (pic included)?

Ouch That's gotta hurt!! After sun won't help! take some neurofen for the pain and fever!! Sit in a cold bath for as long as you can... or cover you legs with a cold wet towel. Make the towel cold when the cooling effect wears off. If your legs are as hot as they look the water on the towel will heat up fairly quickly. .... and what ever you do rehydrate!