I am sorry to hear about your issues.
This is way more technical then anyone could answer here I believe and something you should be working with your doctors on.
"Lately I've been getting very light poop. I'm wondering If CSF fluid can do this?"
I really can answer this, hopefully your doctors can.
We might be abloe to offer some suggestions on the constipation side of things. And chatting is no problem. ;)
But this is outside of my knowledge on IBS for sure.
I hope they can help you and offer some advise and answer some of your questions and sorry to hear your having these issues.