He also might have caught his first nursery d&v bug. They're never that much fun, but unfortunately a feature of having social contact with other kids at that age, especially if a bit short of vitamins.
As I understand it, the rules are:
Watch the fluids and if he gets floppy or lack lustre then zoom to the out of hours gp.
As far as I can tell, they don't do anything unless the kid is so dehydrated as to be floppy, in which case they put in a saline drip until the child is strong enough object to the drip line.
If there is a temperature that won't go below 38 degrees with calpol then that's an antibiotic job.
Everything else in my experience, just has to be ploughed though, but with plenty of care and attention over fluids.
Take care there. It's not the most fun this kind of stuff. 