If you only have a bowel movement every other week you are already extremely constipated. Change you diet before you try to do any P and B shakes. Read about foods that kill and foods that heal on curezone.
Start drinking at least half your body weight in ounces of water every day.
Removing what ever is in your colon will help, however, you must address your diet. What ever you are eating must not be good for you. I cannot imagine how badly you must be feeling only having a bowel movement every other week.
I would consider doing a few enemas to get going too.
Hopefully others will come in and respond to your post.