My GP thinks I have ME/CFS but a different doctor I saw thought I should have a muscle biopsy for MD.

Basically my symptoms are muscle weakness throughout and acute fatigue. Most people with ME have these symptoms but others as well. I have just these two symtoms tho my muscles are so weak I can only walk 100 yards or so and I cant sit up properly for more than a few minutes. This is really hard to live with so any advice would be very much appreciated. Thanks. Paul.