I disagree completely, Velmy.
Fibromyalgia sure as hell exists as a physical thing. It can often be traced back to a physical injury, an accident, from which the body never fully recovers, so it is left vulnerable to further ongoing small-scale daily damage from everyday activity, which results in pain and fatigue.
It used to be called FMS, Fibromyalgia Syndrome, and I think it's useful to go back to that idea of it being a cluster of symptoms.
Not all sufferers have all the symptoms, but there are commonalities - the fatigue, as in limited stamina; pain not in the joints but where the soft tissue attaches to the bone; migraines; some difficulty with words and comprehension; flu-like symptoms on waking; etc.
I don't believe there is any treatment, for the simple reason that if they don't know the cause, it's hard to know how to treat the illness.
My advice, OP, is to analyse your symptoms in detail, and see if any of them have a different explanation, and can be treated. Some things may not be related to FM at all, and it can happen that manageable conditions go unchecked because they get swept under the carpet of 'Oh it's just part of FM'.
What's left is the FM. There is no cure, only living with it and through it. The most important thing is to keep active, keep moving, keep exercising, keep walking, keep swimming, anything - inactivity and immobility are the enemy.
Exercise reduces pain- even if feels like a struggle, get moving, get active: the pain on waking, or on exercising, actually eases as your body loosens up.
FM does not affect the joints, so any pain felt on starting to move is stiffness in the soft tissues, you're not doing any damage to anything, and the pain will get better not worse if you push through it.
Mobility: use it or lose it!
Wishing you well, OP - eat well, stay positive.. but above all staying active and mobile, even if it feels like a struggle.