Talk to General Physician on Mild Temperature

Aoa, i want consultation for my father's health. He is 54 years of age. He is having mild temperature around 100°F from last two weeks. Apparently there is no symptoms of fever like there is no sore throat, flu, body aches or headache. He just feels cold. when He took fever medication from one of family doctors for five days, fever got down but again it went to 100 and he feels cold. kindly give your opinion. it would be highly appreciated. Thank you!