Thanks for your query,
Most common cause of fever is a viral or bacterial infection. Autoimmune processes and drugs can cause fever.
As you mentioned you have intermittent fever
for about a month and spite of proper lab investigation doctor has failed to trace cause of fever, it is referred as Fever Of Unknown Origin.
In up to 50% of cases no cause is found.
You should inform your doctor about your work, places you have visited recently,exposure to pets and other animals, family history for possible hereditary causes of fever (familial Mediterranean fever
You may have an ultrasound
, computed tomography (CT) scan, magnetic resonance imaging
(MRI), and Positron Emission Tomography
You can take Acetaminophen/Asprin to suppress fever like.
Eat healthy diet
Drink 6-8 glasses of clean water
Hope it helps.