@suri, I have no medical background or training but I try to rely on doing my own research and finding out as much as I can about a condition I have. While I don't have fibromyalgia I think it's more a matter of some autoimmune diseases are hard to diagnose and it may be more a process of elimination which I don't think is easy for any patient to deal with. There is a lot of information out there supporting that fact that fibromyalgia is hard to diagnose.

Fibromyalgia: Understand the diagnosis process
--https://www.mayoclinic.org/diseases-conditions/fibromyalgia/in-depth/fibromyalgia-symptoms/art-20045401
Why Fibromyalgia Is So Hard to Diagnose
-- https://www.health.com/health/condition-article/0,,20326400,00.html
Diagnosis - National Fibromyalgia Association (NFA)
-- http://www.fmaware.org/about-fibromyalgia/diagnosis/

It's good that you are being your own advocate. Sometimes you have to seek additional opinions if your doctor isn't listening to you or at least start the discussion with them about your concerns of the lack of a diagnosis.