it sounds like internal hemrroids. when bowel passes through the spincter muscles it could be causing the pain.
rectal area pain when #2 is low and ready to evacuate. once evacuated no pain except for minor pain when sitting. serious pain in my lower abdomen when i had to (holding) go #1 or #2. pain just when holding. now it has decreased to just pain when holding #2. no fever or other symptoms. no blood in stool i can see pain sometimes radiates into left testical when holding stool before evacuating. i can't relate it to foods but i can say on vacation i did eat a lot of junk i normally do not eat with the kids. it is now 4 months later and i am still dealing with rectal/lower abdomen pain issue only when holding #2.