I had the same thoughts as you and have tried many things, pysilium husk, triphala, lactulose, carrot juice, and many more.
The only things that can produce regular BM's for me is high doses of magnesium citrate/glycerate, enema's, and supposotories.
I have a feeling the problem is not in my colon but further up as that is where my other symptoms seem to appear ( morning gnawing sensation at solar plexus, slight heaviness in stomach, bloating, b-12 absorbption issues(???) ).