First question for you is, do you have service in the Southwest Asia? If so this will help:
Qualifying undiagnosed illnesses or diagnosable chronic disability patterns, that appeared either during a qualifying period of active service or prior to December 31, 2016, must meet the following conditions:
There must be no other cause for your disability or illness than service in the Southwest Asia theater of military operations.
your disability existed for 6 months or more, AND
If your disability or illness did not appear during active duty in the Southwest Asia theater of military operations, then it must have appeared prior to December 31, 2016, to a degree that is at least 10-percent disabling (for VA rating purposes).
Diagnosable Fibromyalgia
This link will give you all of the information:
http://www.benefits.va.gov/COMPENSATION/claims-postservice-gulfwar.asp
This link will define the Southwest Asia/Gulf War service areas:
http://www.publichealth.va.gov/exposures/gulfwar/military-service.asp
If you have service in the defined areas, then file a claim for Fibromyalgia under the environmental hazard due to gulf war service. If you file a FDC claim on Ebenefits, there is an option when you add your disability to select the environmental hazard option from the pull down menu. Just get a copy of the your diagnosis and upload it with your claim.
I hope this helps you.