Have they mentioned doing a test for bile acid malabsorption? I have chronic very watery diarrhoea with that and have been helped a lot by bile acid sequestrants. Worth an ask if it's an option for testing if they can't find any other cause.
The burning, soreness and itching is horrible. I have flushable most toilet wipes, I get the kids one Wilkos as much cheaper and not perfumed or anything like that. It can help you clean the area more comfortably than loo paper. It can sting a little and best to gently dab rather than rub but can be nice and cooling.
I've resorted to placing a few sheets of loo paper or kitchen roll between my bum cheeks before now when really burnt. Needs changing very regularly (not hard with chronic diarrhoea though!) but can help in an emergency if out and about.
I find Sheriproct is great stuff as it has some anaesthetic in it! It's a gel and on prescription. Much less messy than things like Sudocreme or Metanium which tend to get everywhere, are a beggar to clean off and Metanium stains things yellow. I find applying it via a few cotton buds held together tends to make things easier and less sore. You can get sudocrem in a mousse and little tube which are easier than the large pot when out and about, the tube is handy size to slip in a bag unnoticed.
I find getting air to the region can help and letting it breathe and light cotton underwear which isn't tight fitting.
Keep an eye on the outer area as I've had a yeast infection develop on the burned bit before now after really bad bouts of diarrhoea.
Due to blood and mucus, especially after antibiotics making things worse and previous times GPs could find no evidence of any piles on their examination. My gastro consultant said it didn't they were there, had an endoscopy earlier and he was absolutely right! Found 6 and had bands put on.
Feeling rather uncomfortable, forwent any sedation etc... and wasn't the most pleasant of experiences so hoping it will help! Worth it if it helps even some of the discomfort though! I'd have thought they would have seen them on the colonoscopy though, I remember them only finding and removing a polyp my last one a few years back.
I hope they find a solution for you, it can be absolutely miserable and not something that's easy to talk about.