A fever is often the first sign of infection. It's your body's normal response to infection, a high body temperature will normally be shaken off within 2 or 3 days
Wikipedia advises that normal (orally measured) body temperature is 33.2 - 38.2ºC (91.76 - 100.76ºF).
This temperature will naturally rise and fall during the day.
The Wikipedia page devoted to human body temperature mentions that body temperature is normally lowest at 4am and highest between 4pm and 6pm.
Fevers with no obvious cause can be an indication of underlying problems, so as with any health condition if you're the least bit concerned always seek professional advice
