We find even the cheaper digital thermometers from Walgreens do pretty well.

I finally put one in my first aid kit now that I'm a Boy Scout leader. The digital ones last a looong time and are much easier to use. Most kids have never seen any other kind - other than those ear ones.

He may not have that high a fever. It may be that something is just messing up his thermal regulation system and his body "thinks" he is hot.