You're probably just "going too fast." According to Robert Gray in the Colon Health Handbook, you control the dose of whatever cleaning agent you're taking by observing the number and quantity of your stools. If you get stopped up, that's a sure sign you're taking too much. If your stools are about like they were, you're taking too little. If you're taking the right amount, the number and quantity of your stools are increased, and you're probably passing some old mucoid matter with nearly every stool. You can recognize stools containing old mucoid matter (mucoid plaque) by an unusually strong odor, an intermingling of different shades and textures, if they're atypically dark in color, or have shapes other than smooth and cylindrical.
You mentioned that you're doing a colon cleansing program AND P&B shakes. You're probably just overdoing it. Slow down, be patient, and back off to a level that produces an increase in the number and quantity of your stools. And stay there until your stools return to what they were before the cleanse. Then you can increase your intake of whatever product you are taking to cleanse your colon.