Is it a cold or the flu? Karen Judy, MD, of Centegra Primary Care says the flu is an upper respiratory infection that occurs most often during the winter months and begins quickly. The flu’s symptoms include a sore throat and high fever followed by a cough, severe fatigue and loss of appetite. A cold may have similar symptoms, but it begins more gradually and causes a low-grade fever. Dr. Judy says if you are unsure whether you have the flu or a cold, you should contact your physician.