I too have been having the same problems with neck pain, headaches that are caused by the tension in my neck and the middle of my upper back... I have been going the the chiropractor and it feels good and soothes it some, but within the next few days the pain comes back. I know I have mild scoliosis so that may contribute some to it but other than that I have no other explanation than Fibro.
I don't really have any answers for you. It may just be residual pain that flares up at times from your accident. I have an old ankle injury and every once in a while it flares and I can't walk on it for a few days. I am sorry you are having such pain. I understand the frustration of not knowing what the deal is. Did they x-ray the area, and do nerve tests on it? I hope you find an answer but there really may not be one.
One more thing, do you really believe you have fibro? If you know you do, and don't just think the doctor labeled you with it for loss of any other ideas, then the pain really could just be fibro pain. Which, by the way, really sucks. Good luck!!