Sorry for injecting science into this discussion but here is why you should not be devastated.
Again, I'm taking your post for face value.
Someone at your height and weight probably has a daily energy need of around 2000-2100 calories. Assuming a bit of metabolic slowdown you probably have daily energy needs around 1900-2000 calories.
The IP protocol has you consuming around 700-900 calories. This is a daily deficit of around 1000-1200 calories which means you should be losing about 2lbs of fat per week. These calculations are never precise - just a ball park.
In the last six weeks you've lost 1 lb a week for a total of six. Science tells us you should have lost 12.
Due to the amount of weight you lost for the first several months it is unlikely that you have any kind of hormonal challenge that would suddenly slow your weight loss.
Therefore, the most likely reason this is happening is water retention and most likely you're due for a "whoosh".