I have high fever (100f) coming and going,started with a runny nose but now have dry cough.no aches though.covid tested negative.what could be the other reason?

There are dozens of respiratory viruses that trigger such symptoms. They are often never defined since these issues usually self heal over a week or so.

If you develop high fever, shortness of breath, prolonged cough, a re test is recommended. If these signs develop see your PCP. If severe see urgent care or Emergency room. Treat symptoms, isolate until well.

Fever itself is not a dangerous sign, if the patient is otherwise walking, talking and eating. Runny nose and some cough can be due to many common viruses, mostly not dangerous. It must be a relief to be COVID negative, but if your symptoms worsen, e.g. abdominal pain, shortness of breath, chills and tremors, please see your doctor again and as recommended, consider repeat test.

Dr Ferranti agreed