Are you aware that you are only taking in 700 calories??? 1 Tablespoon = 100 calories. That's why you are losing weight! No one can work on 700 calories and NOT lose weight.
You could consider doing a juice fast with unlimited juice and water in between. I am quite honestly very hesitant to recommend that though, as you would probably continue losing weight. A juice fast is, however, more nourishing than the Master-Cleanse and not quite so monotonous, so it might be easier for you to get enough calories to stop losing weight.
In regards to 3500 - 4000 calories a day - it sounds like you had a Tapeworm or something similar (unless you are an athlete). Most people who I have met who struggle with their weight like that often do have something like a Tapeworm feeding on them.