ummm his rash is eczema i think but at one stage we got sent to womens and childrens hosp to check it wasnt staph or strep it was soo bad. his lymph nodes (is that what their called?) are up around his ears and neck which the GP said could be related...
Sounds like your LO could do with a full check-up, JIC. Most newborns get a hormonal rash a few weeks after birth that lasts a little while, but that's from Mum's hormones, not from an illness. Not sure if it could be that?

If he's not well, then more frequent bfs are a good option, for both putting on weight and helping him recover.

You're doing a great job to keep such a close eye on him and keep bfing.