(As I'm pretty sure that I mentioned in the previous post I'm pretty bad at explaining illnesses so here's something that explains it better then I could have)
Taken from the Athritis Victoria website
Fibromyalgia is a name given to a group of symptoms marked by generalised pain and muscle stiffness. These symptoms can be felt in all different areas of the body. Extreme fatigue (tiredness) and sleep problems are also common in fibromyalgia. Fibromyalgia does not cause inflammation or damage to the painful areas, but seems to be due to an overactive pain system. Fibromyalgia is different to polymyalgia rheumatica, a type of arthritis that causes inflammation in the muscles.
If you'd like to learn more - symptoms, cause, managment etc - I highly recommend checking out the website. Follow the link at the top of this entry. It's all on the one page.