Hi, Redial, and welcome! The MRI is a good test, from what I have heard. If you have MS I believe they would see lesions on your brain. Also, I'm sure they did blood work to rule it out, too. We have to have quite a few illnesses to be ruled out before a diagnosis of fibro is given because we have many of the same symptoms as other illnesses that they can test for.
Be sure to read Fibro 101...the first thread on the forum. There are links to good information about fibro and you will learn a lot there. There is a link called What Else Could It Be. This will show you what they are checking for with all of their testing. Also, The links called Symptoms and a Thorough Explanation of Fibromyalgia are good starting points, too.
I'm looking forward to getting to know you better. Don't hesitate to ask questions because we are here to help you. I hope to hear more from you soon.