Unfortunately there is no blood test to take to determine of you have FM. A skilled doctor rules out other possibilities with blood tests and then determines, based on your symptoms, if you have FM or not. Some doctors rely on something called pressure point testing; they press on different points on your body and if you feel pain in many of them that's a strong indication that you have FM. (Unfortunately some people who don't have all these pressure points also have FM). 

FM is often also accompanied by difficulty sleeping, concentrating, fatigue, headaches, upper body pain, reduced ability to exercise, increased sensitivity to odors, lights (stimuli) and, of course, widespread body pain. 

We have a nice section here on Health Central on FM. 

http://www.healthcentral.com/chronic-pain/fibromyalgia.html

If you need to find a doctor knowledgeable in FM you might what to see if there's an FM group near you that can recommend one. 

http://www.fmaware.org/site/PageServer