There are several theories on the cause of fibromyalgia but you have to keep in mind that these theories about the causes of myalgia are merely speculative.
One of the theories states that it may be caused by the reduced effectiveness of the body's natural endorphin painkillers and the increased presence of a chemical called "substance P." Substance P amplifies pain signals.
Another theory states that fibromyalgia is caused by biochemical changes in the body and may be related to hormonal changes or menopause. In addition, some (but not all) people with fibromyalgia have low levels of human growth hormone, which may contribute to the muscle pain.
As I said earlier, the cause of fibromyalgia is still unclear, but there are some factors that may result to fibromyalgia, which are;
Genetics. Because fibromyalgia tends to run in families, there may be certain genetic mutations that may make you more susceptible to developing the disorder.
•Infections. Some illnesses appear to trigger or aggravate fibromyalgia.
•Physical or emotional trauma. Post-traumatic stress disorder has been linked to fibromyalgia.