sounds like strep. I used to get it all the time as a kid and I always had the white spots in my mouth/throat. I second the suggestion to call, though. Hope it's nothing serious!
In the back of his mouth, or all the way to the front? I've always noticed white patched in the back and on the roof of my mouth whenever I get a particularly nasty virus.... but that would be something I would say you should visit a doctor for, just in case.