I echo the advice of going by the book, especially if this is your first MC.
Today is day 8 for me and I've lost 17.7 pounds. I lost a lot in the beginning which was water weight of course and now I fluctuate from as little as .4 per day to over 2 pounds per day. I do the Master-Cleanse by the book. I was planning to go 21 days but today I was really crabby and craving food. I am taking it a day at a time. I would like to lose another 30 pounds but that isn't an Master-Cleanse goal in my view--that's a long term goal that requires post Master-Cleanse vigilance.
Don't be so hard on yourself by setting yourself up for expectations that cannot be met. Take it a day at a time, keep it simple and listen to your body and read read read.