That is a mild fever ( I think in terms of Fahrenheit...98.6 plus minus 1.3 degrees normal range --- 37.9 C = 100.2 F) so yes mild fever ..
Do you have cough ?
Shortness of breath?
Muscle aches ?
Other factors and symptoms as to HOW SICK you feel would more determine your need for medical attention ....
Adults do not run a fever as easily as do children and the younger age groups ....
So a minor cold would not as likely cause you fever ...
So I think if not doing well by tomorrow see your doctor for evaluation
The temperature alone is not that terribly high ...
It could be case of flu or sinus infection ,bronchitis as possible scenarios ..
I hope that this information is helpful for you
Let me know if you have further questions or concerns or discussion
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Thank you and Best Regards,
Anthony Bray MD