I’ve dealt with this for several months and it is HORRIBLE. Fortunately, mine is cleared up. I found that the only really sure way to treat the symptom was to follow the diet and protocol, but also to really really thoroughly rinse your butt, as far up as you can, with water to get all of the residue from your stool off of the rectum. It’s the residue coming out of you that is irritating the rectum.
However until you clear it up internally, you’ll be fighting an uphill battle, so start with diet changes and follow the prototol.