OP said...
I suddenly experienced severe rectal pain which made bowel movements very painful and also meant I was suddenly struggling to insert topical meds due to the pain. Worse still, the pain persisted after BMs for sometimes hours afterwards and the pain was severe enough to stop me sleeping.
At first this pain sounded like I had possibly had a fissure, but then I found a small external lump
around my anal opening which was sore to touch which I then wondered if this could be haemorrhoids. A visit to the emergency room suggested that the lump was probably swollen lymph glands that would improve once my UC was brought under control.
Get a 2nd opinion, this time from a GI who specializes in UC rather than a non-specialist working in an emergency room.
I once had severe rectal pain that was at first diagnosed as hemorrhoids. Each BM was a torture chamber that felt like I was expelling shards of glass. I doubted that hemmies were normally that painful so I got a 2nd opinion which determined that I had a perianal abscess.
The GI drained the abscess and placed me on a three week course of Flagyl (antibiotic). That was years ago and I haven't been bothered since.