@fify-- Whiplash pain and headache may or may not be a sign of concussion. You should be seen by a doctor to make sure that you didn't suffer an injury to your head or neck.
Even a minor car accident can cause serious injuries to the neck and head, so please don't take this lightly.
If everything looks normal during your check-up, then just rest and take a pain reliever. You might want to consider wearing a soft cervical collar to keep your neck immobilized so that it can recover faster.