Ultrasound has limited sensitivity and specificity (low diagnostic value) for diagnosing Hashimoto. You may need thyroid antibodies to diagnose Hashimoto.
Fatigue and weight gain need investigations for;
Connective tissue diseases
Chronic infections like Epstein Barr virus
Endocrine diseases (Addison disease).
Chronic fatigue syndrome
You would need the following investigations:
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
I hope your symptoms resolve soon.
I would be happy to assist you further if you need any more information.
Thanks for using Just Answer.