I've had fissure-like pain over several years, I put it down to poor technique and stress. Seen docs here and there that thought it was haemorrhoids and treated with prednisolone cream (Scheriproct). It would come an go, I'd use the cream and be fine for a few weeks and the cycle went on.
About 18months ago it got worse and just wouldn't get better, went to a doc and confirmed it was a small fissure at 6'oclock. Burning, scratching sensation and muscle spasms. Was worse after a BM and just sitting down for any length of time would make it worse too.
Tried Nifedipine cream for 2 months, didn't clear up so had botox injections.
The botox helped the spasms, but the burning pain stayed. I was booked in for a LIS, but the doc examined and said there was no sign of the fissure - it had healed. Very surprising as I felt the pain hadn't gotten any better. I've since confirmed with another doc that there is no sign of the fissure.

I still get a burning sensation and particularly after sitting for longer periods, in the car, at work etc I get a deeper aching pain.

I've seen a pain specialist and tried a ketamine/amitriptyline cream and also a nerve block at the base of my spine, neither had any impact.
I've seen two pelvic floor physio's and they identified my hypertonic pelvic floor and did some tests to confirm. They offered some exercises and floated the idea of gentle stretching - But I just don't make any progress with the physio.
I've had 3-rounds of botox during this time and it does provide some help for a few months, but doesn't take away the pain and discomfort.

The burning, scratchy uncomfortable feeling is the same now and when I had an active fissure. It feels like there is a fissure, it's uncomfortable all the time - particularly when sitting down.
It seems I have exhausted treatment options and to be told there doesn't appear to be anything physical wrong, while still being in the same pain....it's hard.