The 'symptoms' that most people experience when doing the Master-Cleanse or any type of fasting/cleansing are related to how toxic the person is. People who have maintained a healthy lifestyle and/or have a particularly strong constitution, regularly neutralizing or eliminating most toxins through their natural detoxification system, will be the fortunate exceptions and not experience the discomforts of cleansing...only the benefits. You may be one of those lucky few!
I am aware that the Master-Cleanse is also considered a bowel cleanse. However, having done the Master-Cleanse myself a few times, and also done repeated Colon Cleanses involving herbs, psyllium and bentonite, I am of the opinion that the MC does not thoroughly cleanse the bowel. The mucoid plaque (black ropey stuff...also brown, gray, green) takes herbs and/or psyllium/bentonite to soften and loosen it, and the mechanical action of Bentonite and a high intake of fiber to dislodge it and sweep it from the intestines. The average adult colon is about 5' long and the small intestines are about 23'. The surface area of the small intestines is about the equivalent of a tennis court! People can have 10-40 lbs of mucoid plaque in their intestinal tract! It takes time and a lot of work to clear it out.
The MC is a great overall cellular cleanse, but you are unlikely to pass mucoid plaque (or at least not much of it) while doing the MC. It doesn't sound like you're doing anything 'wrong' with the MC...it just has its limits regarding what it can rid you of.