As someone who suffered chronically from constipation there is only one thing I can tell you. In almost all cases it is due to a food intolerance. The Master Cleanse will help with it and will alleviate it somewhat but it won't go away. You will need to find out the culprit (in my case it is wheat) and then completely eliminate it from your diet. Then you will have regular BM.
The difficulty is finding the culprit. Once you have found it you will feel better within three or four days.
There are various options of finding what you are intolerant to. The most common one is doing an elimination diet. It is somewhat tedious. There are also some tests, though they are notorious to be incorrect or only partially correct. I was very lucky because I found a Kinesologist who was specialised in this area and very competent - which is rare. That together with trial and error and I was able to eliminate those foods that make me ill.