Hey Jane,
I agree that fibromyalgia is over diagnosed.. Sometimes it's just a scapegoat when doctors can't find a true cause for a patient's suffering..
However, a lot of research links fibro to problems with the nervous system.. My rheumatologist personally believes that it's caused by the overactivity of neurotransmitters in the brain, but there really isn't much medical consensus when it comes to fibromyalgia because there just hasn't been enough research done.. For every study done about fibro, there is another one that refutes its findings..
Fibromyalgia is technically a syndrome (or a set of symptoms) that can coexist with other conditions.. If your body has been "out of whack" long enough, it might very well lead to fibromyalgia or a physical state that resembles fibromyalgia.. That's why a lot of cases of fibro are linked to autoimmune disorders, viruses, intense physical or emotional trauma and other medical distress.. I personallly believe that if your body and brain have to overcompensate due to physical or emotional distress over a long period of time, they eventually just get stuck in overcompensation mode..
Of course, those are just theories and speculation.. I know that there is a relationship between fibromyalgia and chronic myofascial pain too, but I haven't done enough research on the matter to discuss it intelligently..
In any event, not every fibromyalgia sufferer experiences all fibromyalgia symptoms.. Yes, they generally have the tender points, but a doctor could pick just about any point on my body to press and it would hurt.. My most common symptoms are pain, fatigue, anxiety, dizziness/lightheadedness, sensitivity to light, sound & touch and a general feeling of illness.. Everyone of us is different though.. Some have depression, some don't.. Others have IBS, while some are IBS free..
I honestly don't know whether or not it matters if you have fibro.. You're already getting treated for your symptoms & I'm not sure that a diagnosis of fibro would change anything (except your doctor's willingness to look into medical maladies and find the true root of your problem because EVERYTHING can be blamed on fibro)..
Anyway, I've rambled for long enough..

I wish I could help more, but most of the time, I'm just as confused as you are..
Take Care,
Melanie