Hi Ragtop
Sorry your son is having to go through this. Did they actually remove his appendix or are they just trying to manage the infection?
I had an appendectomy 18mths ago and was given Metrodiazanole (Flagyl) while in hospital. I already had mild PN in hands & feet and after the surgery it became full-body intense PN. No one can confirm if it was the Flagyl as I also have an auto-immune condition.
Hopefully your son can avoid PN developing. As others have suggested supplements that may help I won't add any. Re the possibility of him having Crohn's disease there is some work being done in using Low Dose Naltrexone (LDN) to help relieve symptoms. Here's a link:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3962576/
Let me know if you want more info - I have several sites bookmarked.
All the best for getting the diagnosis sorted and getting him the right treatment.