My son has had a fever of 102.8 for five days but it comes and goes. No other symptoms. I don't know if I should take him to doctor or not because there isn't anything else going on.

A fever is a sign of something else that is wrong, a fever does not just come by itself. So of course there is another medical issue causing the fever.

When you say come and go, How, and when? What treatment are you using for the fever ?

Yes after 5 days, I would take him to the doctor.

I have been giving him ibuprofen once a day because he only gets fever in evening time.

I would have taken him a few days ago. Why wait?

Obviously he needs to see a doctor.