HUGE! bowel movements.

I've been doing the pB shakes with a colon cleanser, and having bowel movements every 3-4 days. I am drinking at least a gallon of water a day. The problem is...my bowel movements are literally so huge that they are clogging toilets. They are exceptionally hard, some as large as large apples. Believe me, it is very painful, and I cannot pass them sitting on the toilet. I have to put my feet on the seat in a squatting position and support my anal sphincter with my hands, much like the vagina during childbirth. In fact, it is almost like giving birth. The kicker came when I clogged a toilet at work, the industrial kind of toilet that could swallow a VW! Help! Please!
Martha