Passing Mucus all the time

[OT1997]

Hi, I'm a 20 year old male and ever since a day in mid 2016 I've been passing lots of mucus on its own. I've become severely depressed because of the pain and discomfort of it being held in my anus, and I've dropped out of university because of it (I can't concentrate on anything never mind studying, just had a rubbish time in general). I'm currently going through Gastroenterology appointments and had a sigmoidoscopy/stool tests/MRI scans but this hasn't showed anything. It all happened really abruptly back in 2016 like one day I was fine and I felt really ill one ay and haven't been the same since. Tried all different diets (I had dietitian appointments) doing Atkins/Paleo/Gluten free etc. I've noticed recently the less water I'm drinking the less mucus I'm passing which has greatly helped symptoms of pain - I've noticed that if I drink excessively I will experience symtpoms around 24 hours later and if I drink alcohol, the mucus burns and irritates my anus and is 10x more painful (I take codeine to deal with it). Just wondering if this may be related to drinking - I remember at the time it all started I was drinking excessive amounts of water (3 litres per day) so maybe my gut has developed intolerance to liquid. I don't have any other associated IBS symptoms

Thanks very much