Hi Lyn Marie,
I've done the P&B shake/cleanse thing several times. I recommend taking some sort of natural laxative along with it, as many others recommend on this forum. I personally like the Chocolate Smooth Move Tea by Traditional Medicinals, but there are all sorts of options in pill form or what-have-you in health food stores. I'm not sure I agree that everyone must always use these laxatives along with the shakes, because it's a personal thing---for some people at some times, the peristalsis just kicks in with the P&B (for example, when I'm doing a raw foods diet alongside the cleanse...)---but sounds like in your case it would really help.
To your health!