These investigations point to some infection going on. The other possibility is autoimmune disease.
You may get the following investigations, if not done;
Liver function tests
Thyroid function tests
Erythrocyte sedimentation rate (ESR)
Serum electrolyte level measurement
Immunoglobulin M (IgM)/immunoglobulin G (IgG) coxsackievirus B titer
IgM/IgG human herpesvirus 6 (HHV-6) titer
IgM/IgG C pneumoniae titer
You symptoms can be due to:
Connective tissue diseases
Chronic infections like Epstein Barr virus
Endocrine diseases (Addison disease).
Chronic fatigue syndrome
Apologies for any intrusion of those automatic offers for phone calls. These are produced by the website automatically and outside of my control.