Hi, low grade fever could be due to the allergy to some foods, tuberculosis, exertion if over active. Chronic urinary tract infection, or viral fevers may some times have low fever if calpol is used. I advise you to show him to the pediatrician for diagnosis and treatment. He may need to have tests like T.C, D.C, E.S.R,WIDAL, Q.B.C., and urine examination, and stools for reducing substances. Thank you.