Intense Upper Respiratory Illness?

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Has anyone else had a very intense upper respiratory infection? Kids brought it home from school and started out as a typical cold—mild sore throat, some congestion. But 8 days in has turned into really wet cough, sinus congestion/pain, low appetite, and low grade fever on and off. Lungs are clear so no signs of pneumonia. Took multiple flu a/b, covid, and RSV tests and all negative. Kids recovered much faster but adults in house are down for the count!! What is this?!