Raised white bumps

Jaxon today started getting small areas on his lower back/bum that had a cluster of bites that were red around them... They dissappeared after a while then appeared on his neck then other parts of the body.

They keep dissappearing.. He was a bit cranky but not really and is eating, no temp or anything and having his afternoon sleep now... Given him some pamol just incase...

ANyone have any ideas what this could be???

On his bum there was one big looking bite that could have been like a mosquito bite but then there are the clusters of small ones close by...

Ashleigh had the same sort of thing a month or so back, which kept migrating around her body. The doc said it was an allergy rash and I posted some pics on here (I think it was in First baby and more, I'll see if I can find it and bump it up) and everyone seemed to agree that it looked like an allergy. I have never figured out what from though and she hasn't had it again.