GPs here are just absolutely useless. Have you tried reaching out to one of the specialized clinics? I've been under treatment for ME/CFS at Vermoeidheidkliniek (yeah, not the best name) and all of the specialists there have been incredibly helpful and willing to try different things.
They don't have very good reviews in Google but I can give it a try. My wife is in the queue for the new "Long Covid Clinics" but who knows when there will be room... they opened in November and we didn't hear anything else since then.
