M.F.
My 4 yr old has had something similar going on since Saturday. Spiked a 102, then Sunday 103, then went away Monday morning when we took him to the dr (our daughter just had strep, so we thought it might be that...). Doc said it's just a virus and that she's seen a lot of this random fever lately. His temp came back up to 101 or so Mon evening, then went away again Tues morning. We thought it was gone yesterday, but he went to bed with a 100.4 or so. He's had these random viruses before, and they can take 5 or so days to run their course. It's very frustrating! We're hoping that today -- day FIVE -- is the end of it! Luckily, it seems to be getting a little better each day.
The flu is an upper respiratory thing, so if he's not coughing, flu is not likely. You can check out the symptoms and info at www.flufacts.com.
Strep is a possibility, but that's also really painful, and the fever stays high instead of bounces around, and he would be very sad and wouldn't eat or drink much.
That said, 5 days of fever is probably worth a phone call to the doc if you're worried.
They can at least give you some parameters, like if he still has a fever after X days, or developes X symptom to come in.