Hi 3STL!
It's typical to start off a diet in which you start drinking more water with running to the bathroom, lol! It happens to all of us. Also, its not uncommon to be focused on food when you're dieting. After all, we have to be mindful, when before, we didn't give it much thought. We just ate what we wanted! I don't know anything about the Cambridge Diet other than, if I remember correctly, it alternates higher calorie days with very low calorie days. I know there are a few people here who do Intermittent Fasting and I think they do that too, so if you can't find anything on the Cambridge Diet specifically, maybe you can look in the IF forum (under the Diet Central section) for tips. Many of us here know the frustration you're describing--not feeling like yourself anymore, not being able to fit into clothes, etc.--and you will find lots of support to help you reach your goal! Good luck!