Sounds like he is coming down with a bug of some sort, but the temp is not concerning at all.
Keep an eye on him and keep his fluids up - food is not really important, but hydration is.

Lots of cuddles and lots of water and love.
If his temp goes above 38 or so, then I would be concerned, otherwise, he is just a bit sick, nothing to be scared about. Sounds exactly like how Charlotte gets when she has a bug, we had a day of it last week, then the next day she was fine and merry again.