It is the worst pain I have ever experienced! I am so sorry you're in the midst of fissure hell. I actually have written several posts that included my horrors with it.
Sadly, nobody believed me. I went to the emergency department so many times (sometimes waiting to be seen for 8 hours!!!). I had a colonoscopy and asked my gastro to see if he could find the source. Not only could he not find it, but he asked a surgeon to step in and have a look. The surgeon didn't see anything. Nevertheless, my gastro set up an appointment for me to see the surgeon about it. I did. This is when the surgeon walked into the room, took one look at me and stated, "There's NOTHING I can do for you." You may gasp now. That was the coldest encounter with a doctor I've ever had. I was crushed. I literally cried.
I asked my gastro if he would set up a consult with Duke University in Durham, North Carolina. "No, I really don't like to do that. They are really funny about that. There has to be a lot of documentation for that, and I really don't deal with 'that' area." OMG. Another gasp if you wish, lol. So I went to my primary care physician. He said he would set it up!
I was seen by a colorectal surgeon. My experience at Duke was phenomenal. The surgeon apologized for the pain during the anal scope exam, as I begged him to take all the time he needed to find the source. It was over in no time. "Jimmy, I see the source of your problem...it's an anal fissure." I asked, "Is there any way two doctors could have missed this on entrance and exit for a colonoscopy?" He replied, "Not unless they just weren't looking!"
I didn't opt for any surgical procedure due to the risks of fecal incontinence. He told me that he didn't recommend anything invasive due to where it was located. I don't know how, but it healed on its own! Suddenly "shitting razor blades" as one doctor described it was a thing of the past. I did, however, buy a bidet toilet seat. OMG. You cannot know the difference it made in my life. Best investment I ever made. I'm sorry this was so long. I do hope you find relief and that it becomes a faint memory, never to be revisited.