What on earth is going on?!?!

DS had his temp and spots Thursday, still has spots today but had been fading. We went out today, get home and bath the kids. DS sits on the couch and becomes really hot really quickly. Within half an hour his temp had reached 39.1 after having no temp since Thursday arvo. He was quite flat today but we thought he was just tired.

Why has his temp gone up again after a couple of days without one?! (We haven't given him panadol or nurofen since Thursday night)