Welcome to HCM
for more than 2 months itself is serious enough to find out cause for it some times such prexia of unknown origin is challenging task,as count is high a trial of antibiotic is warranted but as she is also suffering from hypothyroidism
so some kind of autoimmune disorder should be considered .
It is beyond the scope to point out all the causes but advise would be to get a meticulous physical examination with detailed history.
A stepwise investigation should be planned
Or she may be hospitalized and investigated for the cause as waiting too long may be deleterious for her.
Many times atypical infectios,inflamatory diseases and hidden Tuberculosis
and malignancies turns out to be the cause of unexplained fever.
Good Luck to her.