I've never done Cambridge diet but didn't want to read and run! Maybe pop over to the Cambridge diet forum and ask there, there'll be some people who will be able to answer your questions more than I could.
One thing that I find helps me when i'm really struggling generally, drink a glass of water, go for a twenty minute walk and listen to some upbeat tunes, I have a good think about why i'm doing the diet and what I want to acheive and imagine wearing that gorgeous dress at my graduation and it seems worth all the struggles! Sorry, a bit of a flighty answer, but just know, you're not alone!