It could be; stiffened muscles - particularly in the upper body - are very common in FM as are headaches. On the other hand there's a real danger in ascribing all ones symptoms to FM. Studies have shown that chronic fatigue syndrome patients, for instance, often have undiagnosed - and treatable - problems that they've ascribed to CFS. So, while these symptoms do fit in with a FM profile its always best to check with your doctor when new symptoms arise.

You might try stretching and relaxation exercises, massage or other therapes to try and relax those tight muscles. 

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

Good luck!