fever on it's own is nothing to be alarmed about. It is the body's natural way of fighting things. I would get a fever checked if after 48 hours it was unchanged. However, if the child stopped drinking or producing wet nappies or showed signs of lethargy (above normal "I'm sick so I'm tired" lethargy) or showed signs of dehydration, I would get them looked at sooner.

Sounds like you're doing all the right things. You could also try tepid washes (not cold water but not warm). Just keep in mind you don't want to cool your child down too much as this will cause them to shiver which actually increases temperature.

FWIW - my DD recently experienced something similar. She was spiking up to 39.9 temps, stopped eating and drinking, was HOT to touch, and just wanted to lay on the couch all day. It took her two days to pick up and another 2 to get back to normal altogether (so 4 days total). We originally thought she had a UTI as she was complaining of pain to bladder region but the specimen came back clear.