The wonderful thing is that there's a pattern! And you can work with patterns.
You've realized that you have a crisis day at 20 days. Plan ahead for that day....make it full of primal rich food and non-food treats for yourself. Go to the spa and get pampered. Make it a day to look forward, not to dread and find yourself caving again.
I was borderline for an eating disorder for many years. I would eat insane amounts of milk chocolate, feeling like I had no control, doing it in private, feeling awful about it afterward, using exercise to ensure I didn't gain weight. That's ALL gone now. GONE GONE GONE! So it's really worth it to push through these early weeks. Life is so much less stressful on the other side.
Zone diet on and off for several years....worked, but too much focus on exact meal composition
Primal since July 2010...skinniest I've ever been and the least stressed about food