My 9 year old son has had a low grade fever (99.5 - 101.5 by forehead scanning thermometer ) on and off for 10 days now. I had him at the doc at day 6 and his chest, throat , ears, etc normal. Fever still persists. He is falling asleep on the couch, exhausted by the evening. At first there were no other symptoms, but in the last 2-3 days he has gained a decent cough and loss of appetite . At what point should I be concerned and re-visit doc? Thanks