I do not have your main issue, but FODMAP helped me find some food triggers that cause me discomfort. But it was more generalized discomfort/bloating vs. rectal pain. Not sure what the diet will do for lower rectal pain?  But good luck with it. My main issues are with fructose and galactans. 

Look into a pelvic floor trained physical therapist.  You may have increased tone in your pelvic floor which contributes to the rectal pain. I had rectal and abdominal pain, which both strangely resolved after dealing with my pelvic floor.  I say it's worth a good try versus going under the knife again. Get a referral by your doc...if not specialist then PCP.

Thanks for the input.  I will check into this with my dr.

For me it took about four weeks of  PT to get them to work on it, plus I got exercises to do.  Now I do the exercises -- not labor intensive.  ;-P  I really hope that helps, because I really think pelvic floor dysfunction after all the trauma our bodies go through is often just not the top of the differential because it isn't 'life threatening' if that makes sense.