Following are the possibilities of the causes of fatigue;
Connective tissue diseases
Chronic infections like Epstein Barr virus
Endocrine diseases (Addison disease).
Chronic fatigue syndrome
You would need following investigations (some must have been done):
Complete blood count (CBC)
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
Please feel free for your follow up questions.
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