Generally lower back pain on the MC is not really back pain but it's your kidneys. The MC is considered a kidney cleanse and while it might be a bit alarming it's actually a good sign that you are releasing toxins or maybe even kidney stones. Just keep drinking lots of water.Cleansing/Detoxing is not always a bed of roses. It's quite common to go through a "healing crises". The wisdom is not to quit but to continue to fast your way through it to allow the system to eliminate the toxins and do it's healing thing
Something that helps the kidney discomfort and helps them eliminate more toxins is doing hot ginger compresses. Just take ginger and grate into a pot big enough to put a towel in it. Boil up the water and ginger for a few minutes. When it cools down enough that you can stand putting your hands in it, soak a towel in the mix and wring it out. Fold it in a size shape to cover the affected area on your lower back. cover the towel with piece of plastic and put a couple of towels or a folded blanket over it to retain the heat.I'm sure a good hot bathtub soak with Epsom salts would be soothing also. The E salts also help draw toxins form the system. Just keeps drinking lots of water to keep things moving.
Generally after the system has emptied the contents of your bowels which takes around 3 days all that will be coming out is yellow orange "butt pee". I have no idea what book you are talking but it certainly is not Stanley Burroughs book. The SWF producing yellow/orange liquid butt pee is completely par for the course after the 3rd or 4th day