I wanted to welcome you to the board...I'm sorry you're having rectal spasms that last for hours! That sounds awful. I have felt those on occasion, but like other people, only for a few seconds. You might ask your doctor about pelvic floor dysfunction. The pelvic floor muscles surround the rectum and sometimes various times of nerve dysfunction in the area can cause problems such as rectal spasms, pelvic pressure, and problems with urination or having bowel movements (not necessarily all of these).
If medications have failed and you have other abnormalities ruled out, you might have some luck going to an osteopathic physician (DO) who can do manual medicine (I'm an osteopathic medical student, which is why I bring this up). We have been taught about sacral dysfunctions that lead to symptoms such as these, and there are manual techniques (in which the doctor would work on your pelvis and sacrum - not your rectum, don't worry!) that can help if there is a sacral torsion. Since they are medical doctors, they can also prescribe medication if necessary. They'd probably give you some suggestions about exercises you can do to relieve some of the tension in your pelvic floor or refer you to a neurologist if it is, in fact, directly related to a nerve injury. It's just another option to think about, since it appears you haven't had much luck with the meds you've tried.
Hang in there and let us know if you have more questions.
Co-moderator - IBS Forum