Salamon, the pain that you experience after a BM from spasms is one of the really nasty side effects of anal fissures. I too had these and they went on for close on 2 years before I experienced some relief. Just happened gradually that the pain decreased.
Please do read pinpin and Davo's reports of their surgery. The are really two of the best ones on here, written clearly. Also, as I said before, the vast majority of those who come here have had surgery, left the forum and are busy getting on with living life again
It is probably a good idea that they do a colonoscopy so that they can make sure that nothing else is wrong, and as you said he is an experienced surgeon I am sure he is doing what he thinks is best. Another good thing; you have caught this when the fissure is relatively acute. Much the best. Many of us leave it much too long before seeing a CRS.
I too used both Nifedipine and Diltiazem, though the are both close to being the same in that they are both Calcium Channel Blockers. Eventually they both gave me a rash so had to stop. I never tried Rectiv, which can induce headaches in most people. I never used Miralax. I use Milk of Magnesia. What helped me through it all was the ability to get through the night with the help of a very low dose of Lorazapam. Don't know what I would have done without it.
Anyway, good luck with your colonoscopy.