What could be the possible reasons for these fever outbreaks?

Hello,

In order to answer your question, I need to validate some information.

How is his sleep generally?

How is his general condition during the day?

Does he have any other symptoms? Earache? Nasal secretions? Coughing?

If no other symptoms are apparent at this time, you did the right thing by making an appointment with a doctor. We can tell from your description that something is affecting his overall condition. A medical evaluation is required to find out what is wrong. In the meantime, the use of painkillers like Tylenol or Advil/Motrin and good hydration will help make him more comfortable for the night

It was my pleasure! Have a nice day