Second poops that won't come?

Ugh. Pretty much 99% of mornings, after I have my first BM, I feel very uncomfortably incomplete until I have a second BM. On a good day, I feel "done" after this; on a bad day, I still feel somewhat bloated. However, without that second poop, I am so massively uncomfortable all day.

This has always been the bane of my mornings, and makes me late for practically everything, since I can't control when that second BM will come. I used to be able to sit on the toilet and coax myself to relax until I finally got the urge to go again, which could take anywhere from 10-30 minutes, and that's after waiting for the FIRST poop to come.

Lately it's been worse in that the second urge so I can go again is NOT COMING. No matter how long I try to give myself. I'm late to everything now, work, social commitments, anything, because the feeling of having an "incomplete" BM is so awful and lasts all day that I am so desperate to avoid it. Sometimes I can go again after eating, but since I'm at work (teacher) this is not an option. Plus it's terrible having to eat anything while feeling like this.

What do I do?? Does anyone else have this problem?

Some relevant points:

I eat plenty of fiber, maybe too much. My dietitian has actually tried to get me to cut down on my fiber intake since it's way over the necessary amount (I have orthorexic tendencies).

Eat mostly whole, plant-based foods

Eat dinner around 7:00pm, morning BM around 7:00am for work days, weekends vary more but morning BMs happening usually 12-15 hours after finishing dinner

I have a squat stool already

Help :(