Routine messed up

It's not that we have an exact routine, just a general guideline. DS goes to bed between 7 - 7.30 and gets up at 6:30 - 7 (if we can stretch it out). Usually 3 day sleeps, 2x45min, 1x1.5hrs.
This week DS has been sick (just a cold). First couple of days, he slept heaps during the day and most of the night (though more broken than usual).
Now he's getting better, but his days/nights are a mess.
He's not going to sleep till close to mid-night, and has just had a 3hr mid-day nap (almost unheard of round here). He's still behaving like he's tired! I fear if I put him back to bed he won't sleep again tonight, but as he didn't sleep well last night he's probably genuinely tired.
This has been the way for a few days, big day sleeps, awake as anything from early evening.
How do I get him to switch his sleeps back to the right place?

Issac's Mum - I don't know the answer, but we had similar evening wakefulness last week, which I think was related to stressed out Mum and shifting to a new place. Could also be something they do at this age as they are almost exactly the same age.

Maybe he is a bit unsettled after being sick. My little one is back to her usually evening routine now as we are have been here two weeks and I'm a bit happier. Took about a week of unsettled evenings before we got back into it. (fingers crossed)

Might be a bit hot too? I think that can keep them up at night too.

I agree a walk in the stroller works wonders, choose a nice shady park. Good luck.