The doctor saw the fissure immediately right inside the rectum. Didn't even need a scope. It's simply a tear in the anus which is clearly visible. So you may not have one.
As to the levator/muscle spasm issue it was invisible. That's likely similar to your problem - you can't see it. It's pretty obvious to me that stress from my old job was the cause but I didn't know that until I had quit and the issue magically disappeared. You might get anal massage - that is a real thing. That might relax the muscle. Sitz baths help because they relax the muscle. It's stress. Don't overlook ANYTHING that might cause you to harness stress. It may not be obvious. But you seem like you are holding your stress in your rectum.
One thing for sure - you need professional help from a colorectal surgeon or maybe even 2-3 of them for different opinions and treatments. Self-healing is clearly not helping you. Make an appointment now so you can get your life back.