Oh here I am again LOL I don't want yo to think I am stalking you!!! But you are posing some great questions that I have specific experience with
My hubby suffered his entire LIFE with constipation.. he was diagnosed at 8 years old with
encopresis. So he spent the next 7 years or so on metamucil ect. They only worked for a little while then he would have to try something else.
As he got older, the condition turned into full blown constipation. He would go 10-14 days, and when he did go, it was painful and massive. The running joke (not really funny...) was that if he was coming to visit, make sure you have the toilet plunger available.
He went VLC/ZC a year ago, and even after over 4 years of Low Carb, the transformation happened almost immediately. He is 100% 'cured' and he eats no grains, no vegetation and no fruit. he 'goes' every 2-4 days, not unlike myself. They are soft and easy to pass (check out the 'bristol chart' and he falls in a 4 most of the time...)
If he does eat something off plan, and it happens (because he is not as carb sensitive as me and some days he is just too lazy to toss the bun...), he does suffer. The bloat and discomfort returns almost immediately.
My 7 year old daughter was a lot like him. Her stools were like hard little round deer turds and she would go every 4-7 days. She would spend a loooooooong time in the bathroom. But since removing the vegetables and grains from her diet as well, this is no longer an issue for her either.
You just have to make sure you are eating enough fat.. that fat will take care of all of that for you, and you already know you should not be eating grains.
There are times when we have to take our health into our own hands, despite what the Doctors might say. I am not sure what I would say if a Doctor told me to do something that made me feel worse or that I know is just not right. I would probably just smile and nod and do what works for me anyway.
Good luck, this is really a learning curve for all of us! You can also do some research on fiber, there is a book called The Fiber Menace that you might enjoy...