If you have knife like pain during a bowel movement, with or without pain for hours after, it is likely a fissure. They can be hard to see, and many general practitioners miss them or diagnose hemorrhoids - so see a colorectal specialist.
If you're having no pain during bms, but pain that starts soon after and may last for hours, you're likely having spasms of the internal anal sphincter. I had a fissure for two months, but even after every doctor said the fissure was healed, still had rectal spasms thatbwere very painful - a burning sensation from which I can get very little relief.
There ARE options to help this!!
First, you can try a topical cream such as nifedipine or nitroglycerin that can help relax the muscle.
Secondly, Botox is an option. They can inject it in the area to help the muscles relax. It has about a 50/50 chance of working, and in some cases can make things worse (causing hems and swelling without relaxation).
Finally, the gold standard is the lateral internal sphincteronomy. It is a very minor surgery (in and out of the hospital) where they make a small incision next to the anus, and make a small nick in the internal sphincter. This forces the muscle to relax, and has a very high rate of success (90% or more). A common worry is that this surgery will cause incontinence - but the chances of this are very very small and nothing to worry about. If you're having rectal spasms, your sphincter is TOO tight, so the surgery will just bring it to normal levels.
You can ask your doctor about a manometry test - this will test the pressure/tightness of your sphincter. If it is high, I would recommend considering the options above.
Additionally, you may want to see a pelvic floor physiotherapist - they can tell you where your tightness and pain is coming from and may be able to alleviate some.
Cheri
After reading all of everyone's problems again, I think I need that lateral tiny incision done to my internal spinchter, I even asked at last appointment...when he told me to do digital manipulation. Well that was over a month ago, I can actually feel the darn thing, it is like a very extreme rubber band and it is not getting any looser? I did read on a GI site from Greece, they make all of their patients do manipulation rather than surgery for 10 minutes
2x per day, and it is 90% effective. Ok I am going to do this 2x per day, with desitin...or coconut oil. I was doing this with only one finger before Colo told me two fingers. I have also looked into anal dialators (watch out, some pretty odd stuff comes up). I think I might order one today, ....these doctors around here are useless...the only other Colo guy to go to I would have to switch medical groups, which I did for this one...I feel like I am a cow with a number. I just went on Medicare, you just have to read what makes sense and rely upon your own findings...sensible things with lots of back up. Like I was doing what the doc told me before I went back.