When you don't enough to meet your bodies needs it actually goes into starvation mode - holding onto every little calorie it can get it's hands on. Not eating enough will also slow down your metabolism. So its a double whammy. When you are sick you metabolism is also affected.

Purging will wreck the lining of your stomach and do nasty things to your teeth. Getting on the scales often is only recording fluctuations of water in your body. If you don't eat properly you will lose muscle. And you want muscle as that burns fat.

The truth is that you have to eat properly in order to lose weight. Juice is not a good option as it is full of sugar. But maybe you need that to off set your lack of real food.

Get real with your therapist and try seeing a dietician to help you understand how your body works might help you also.

Good luck.