Ok, this is about my husband, not Harry.....
Andy suffers from Diverticulitis (awaiting an op on his colon) and he too is on amoxicillin etc. etc. It didn't seem to be helping at all, so we went the 'natural' route alongside it. He has to take a teaspoon of honey every day - just like that, off the spoon.
All I know is - if he forgets to take it, he flares up the following day. I wonder if it might help your little one, obviously in a much smaller quantity? It might be worth looking into
Good luck, I wish you all the very best. Sally + Harry x