Some doctors do believe in fibromyalgia and some doctors do not believe in fibromyalgia.
If one doctor you go to does not believe in fibromyalgia and says it's all in your head and you're imagining the condition then you can see another doctor who does believe in fibromyalgia.
It may take seeing more than one or even 4 doctors before you get one that does believe in fibromyalgia but there are some doctors out there that do believe in fibromyalgia and will provide or recommend treatments for it.
The fibromyalgia has existed for years and most doctors way back then never really much believed in it.
But as the years have gone on and some doctors gained more knowledge then some of those doctors started to believe in the fibromyalgia condition.