I've never used Sonne's fiber so I'm not familiar with the ingredients or its effectiveness. I would hold off on the Bentonite until you get some more fiber. Some people do take it alone...but it works best...particularly for colon cleansing...when you combine it with fiber. I don't think the Bentonite is backing you up...I think it's just the rapid decline in fiber. Since you were in the midst of cleansing it is also possible that some larger pieces of mucoid plague have loosened and are taking their time to make their way through the pipes!
If you want to add the MC...run a search for the Ultimate Fast...it combines the MC, the Colon Cleanse and a parasite cleanse.