Patience my friend, patience. I’ve been fasting every week since January 12th – week 3. One Month you gain some, the rest of the Months you loose – average 0,5 kg or more. So keep up the good work! My BMI is normal now, but I’ll continue this interesting journey one year in total. This is the only diet that makes me feel good about myself. Thank you!

5:2 isn’t a quick fix and the average loss is only 1lb per week. Weight fluctuates for many reasons, and you would have had to over-eat by about 11000 calories to gain that amount, so it is most likely food in transit/fluid retention.
A gain on the scales does not indicate a gain in fat. My weight can fluctuate by 5lbs in a single day and it is why I don’t weigh myself more than once a week and often less than that as it is easy to be depressed by the numbers which do not tell the whole story.
As Mondkind said, you need to be patient and look at the overall picture. If you are doing it properly the weight will come off.