I have taken herbal combinations including cascara sagrada, but have not used it alone.
I think off and on is FINE for colonics! I think you need a break between at some points, and continue your cleansing herbally, and/or with fasting, which I have found to be THE most effective bowel cleanser, along with colonics.
The Master Cleanse is the most intensive fast, barring water which I think is much too intense for most people to do long term. In order to get lasting results, you really need to do at least ten days of a fasting cleanse. I am enjoying the juices on top of the MC, and have never been hungry or uncomfortable.
Yep, those headaches are classic detox symptoms. Drink lots of water... and I assume you are evacuating your bowels pretty well with the CS?