I think it is human nature that we question everything and say this can not be, but in the long run your best bet is to accept the diagnosis and work toward gaining some knowledge on how to manage any symptoms you are having. Fibro, may be a catch all diagnosis for when doctors don't know what is wrong, but whether it is or isn't, does not really matter.
If you start reading through the back posts and pick up on anyways to deal with the problems you have right now, you will gain strength in knowledge and that alone will improve your heath. If someday down the road another diagnosis is found then just think how far ahead you will be in having the coping skills you are learning now.
So get started posting questions and giving answers to other peoples posts. You will find so much information that is helpful that it will not matter in the least what the diagnosis is because you will know how to calm it and handle it.
By the way welcome to the forum. Glad you found this site and I hope you will stop by often.