Suggest Treatment For Concussion & Stiff Neck

My son was involved in a wreck around 3 and a half weeks ago. he was diagnosed with a mild concussion. He has been having headaches since the wreck. some are mild and some are extremely bad. they never goo away. He also has a very stiff and sore neck. we have noticed that he is forgetting things alot lately. he seems to be repeating himself alot and does not know he is doing this. This has been noticed on the job by co-workers too. My wife and I are very worried about this . Could this be something serious or is it normal after a concussion?