I really don’t ever want to be advising people what to do when they abuse their bodies, but it happens, and when it does, you need to do whatever you can to help your poor skin!
Take an anti-inflammatory such as ibuprofen to ease the swelling and the pain. A cold shower with also help to soothe the skin and remove any excess salt or chlorine which can further dry out your skin.
If you end up with blisters, apply an antibacterial ointment 3 times a day but never pop the blisters. If blistering is localized, you can treat it at home, but if not, move your backside off the the closest doctor for treatment ASAP!
Wear loose fitting natural fibre clothing to prevent further irritation to your poor skin, and please, please, please, never do that to your precious skin again!