First and foremost, fibromyalgia is not a rheumatologic disease in the strict sense. There is nothing wrong with the muscles, the irritable bowel does not signal a major organ problem, and you are not "inflamed." It is very common for those that suffer from fibromyalgia also have other problems such as osteoarthritis, rheumatoid arthritis, low back pain, or even a history of injury. Some claimed that an infection started at all. That could be possible as well.
There is a common thread that binds the fibromyalgia syndrome, and it is unlikely to be just one thing. The progressive array of symptoms suggests that some type of inflammatory response is occurring, most likely in the central nervous system. We will call that central sensitization. This is where chemicals that are processed in nervous tissue are either creating problems, or not behaving in a normal physiologic way. The process of central sensitization was discussed on this page over a decade ago. Unfortunately, not much research available to better understand how to turn off this process. It is an active center of scientific interest, however.