Something is wrong with my dog and the vet hasn't been any help?

Poor guy, sounds like he's traumatized from the car accident. It also sounds like he could have some neurological issues that they haven't found from the accident. It sucks that dogs can't tell us whats wrong and we just have to guess, but it sounds like he is having traumatic nightmares. He probably relives the episode from the car accident whenever he goes to sleep.