A diagnosis of fibromyalgia cannot be arrived at via any blood test and your doctor will likely have arrived at that conclusion as a result of not finding any other cause for your symptoms.
Please visit our fibromyalgia symptoms page for a list of many, though not all, of the symptoms associated with fibromyalgia.
My blog - 'Fibromyalgia or Chronic Fatigue Syndrome' - also mentions some other symptoms that can help you differentiate fibromyalgia from chronic fatigue syndrome, as the two conditions can be quite similar.
For the joint pain, please consider a course of our Atrosan® Devils Claw tablets. They are licensed for joint pain and rheumatic symptoms and may well be of help to you. Just bear in mind that the effects of Devils Claw build slowly over a couple of months and so don't expect overnight results.
Other than that, you may be reacting to a food. As most reactions occur within a few hours of eating a problem food, it might be very useful to keep a food and drink diary for a fortnight in order to see if there is any correlation between what you eat and any subsequent flare ups.
Watch out for the 'nightshade family', which include potato, tomato, aubergine and peppers, as these can cause many people's rheumatic symptoms to worsen.
Please let us know of any explanations you uncover, as many people have 'false negative' blood tests, yet show all the hallmark symptoms of rheumatic issues.