Sunburns are just that, burns. They should be treated like other burns by keeping the burned area clean, moist, and cool. Clean by washing with gentle soap and cooler water. Moist with light moisturizing cream that is NOT oil-based. Try water-based, instead. Cool by not covering it up and not exposing the are to more sun.
You can try non-steroidal anti-inflammatories like naproxen, ibuprofen, or even aspirin according to directions to try and relieve the pain and swelling. Finally, and I can't stress this enough, try not to get sunburned again and talk to your physician about skin cancer screening. One sunburn is enough to "bump" you to the next risk level for it, particularly if you are of light skin (though anyone with any type of skin is at risk).