DON'T eat just lettuce, there are plenty of leafy greens out there more nutritious than lettuce, I f you are going to deprive yourself cut out the cheese..... i think that the issues you are facing have less to do with the amount of carbs/calories you are eating and more to do with your current mindset...have a search for some threads about eating disorders....there are a few out there....
I htink it's great that you have access to a fantastic support site like this one.. use it for the support that you need to help heal your beliefs about food It would also be helpful to decide which paln you will be following for the beginning and stick to it....so the rules don't get confused.