Many people have found that they easily adapt to the 5:2 Fast Diet and start losing weight straight away, others find it more challenging. If you persist it will work, but there are things to bear in mind.
Firstly I would not obsess about weight. What you really want to do is lose fat, preferably around the gut. I would always start by measuring your stomach, around the belly button, and see what happens over a period of time. On a normal diet you will lose a mix of fat and muscle, which is why it is important to up your exercise levels when you diet, to maintain muscle mass. Muscle is more metabolically active than fat; it burns calories even when you are asleep. What is unusual about Intermittent Fasting is that studies have consistently shown that people on it tend to lose mostly fat and very little muscle.
I also think that people have to be realistic about what they eat and drink on non-fast days. You shouldn’t be obsessing about calories on your non-fast days, because that defeats the whole purpose of it, but nor should you go wild.
If you are not losing weight/fat then I would look first at the calories you are getting from drinks on your non fast days. Juices, lattes, alcohol, fizzy drinks, smoothies all contain a lot of calories. If you can move to drinking more water and sugar free tea/coffee that will help. Calories you drink do not satiate. If you eat three apples they will fill you up. Drink 3 apples in form of a small fruit juice and it will not fill you up.
The other thing is you should be moving more. I always take the stairs, even up 7 flights. Get a pedometer. Aim to do 10, 000 steps a day. Most people do less than 5000. A long term study on people who lost weight and kept it off found that those who were successful all increased the amounts they walked.