I would be inclined to skip this type of diet and instead use healthy, balanced eating and get adequate exercise - this is what will take you through the rest of your life, not using restrictions as a lot of 'diets' do. As a warning, altho' it promotes fast weight-loss, it doesn't say that it increases the risk of not getting the nutrients your body requires or that odds are you will lose muscle as well, which is not what is good.
Below are a couple links that you may find useful: www.webmd.com/diet/features/dukan-diet-rev
As far as your weight gain is concerned, everyone will fluctuate during the day, and in the course of the week/month. No-ones weight stays exactly the same. I know my weight used to fluctuate WAAAYYY more than that just in a matter of hours. It could be that you hadn't been to the loo immediately prior to your weigh the second time - it may be that you had eaten heavier (weight) food in the day prior and it hadn't yet passed through your system. It may also be TOM, or you may have consumed more sodium which will retain fluid. There are many variables for this.