DS has an enormous blind spot on his back

[Mousefoot]

It looks very painful. What can I suggest to help?

Hot clean cloth held against it, keep repeating , should help draw it to a head. Some people use salty water some don't!
People often recommend magnesium sulphate but it seems hard to find at the moment.
Sporners corner on here is good for spots /bites etc

Definitely one for Sporner's, especially if he's up for a photo.