Fibromyalgia Support Group
You're not alone in your pain. Fibromyalgia is a condition that can be difficult to diagnose and manage. If you're trying to cope with pain throughout your body, sleep problems, general fatigue, or other common fibromyalgia symptoms, you're in the right place. The community is here for you to talk about therapies and share your challenges.
Gramybear is probably right about the sciatica - this stretches the piriformis muscle, and the sciatic nerve runs right through it, so if the piriformis is in spasm, it puts pressure on the sciatic nerve. Just something I learned in PT years ago.
And definitely don't self-diagnosis - see a doctor and ask these questions.
http://www.webmd.com/back-pain/piriformis-stretch
Make sure a doc goes over you head to toe. You could have any number of issues, other than fibro, and we here can't diagnose, only support.
Neurologists and rheumatologists are the docs usually responsible for FM patients and dx. Rule out the other possibilities. A simple disc compression can cause tons of pain but be an "easy" fix and not be fibro, for example. It may be nutritional, it could be a thousand things, so I re-emphasize, go to a doctor and be sure.
Luck and blessing.