You should try The Master Cleanse first. It'll get things moving and clean you out within a couple of days. The minimum is 10 days and cheaper than what you'd spend on food or PB supplements anyway, so you really have nothing to lose but the crap in your system.
Some people tend to get more backed up from fiber supplements, so PB shakes might make your problem worse. It's why I didn't do Colonix or PB shakes..(do a search, others have complained about this) I went right for The Master Cleanse and the "pregnant" look went away in a couple of days.
The Master Cleanse also gets rid of parasites since you're not eating Sugar and things to keep them alive and it alkalines your body and they can't live in that either.
If you're not satisfied with the results, you could always do the PB shakes afterwards. If you're ordering your stuff online, you could even be done with the Master-Cleanse by the time it gets here.