What can i do for severe swelling and extreme pain in my legs and feet caused by a bad sunburn?

Cool it: If there is no blistering then you most likely have a 1st degree burn . I would not put on any oils etc. I would take an analgesic such as Motrin or aleve (naproxen) etc. I would keep the burn clean and apply cool compresses as needed.

Dermatologist: Ifthere is severe swelling then this would be best treated by your physician or a dermatologist.

Simple Care: Sunburn is response of the tissues to injury from solar radiation. It is inflammation to increase blood flow to the area to promote healing. Do not use ice as this injures already injured skin. Cool water soaks can help as can taking anti-inflammation medicines like Motrin or advil (ibuprofen). Avoid any further damage as this can cause scarring . Good skin cream applied daily/gently helps.Leg elevation helps.