Water retention during the week leading up to your period and on into the beginning of your next cycle is completely normal. Fluctuations of the same manner are often seen around ovulation, too.
Just keep your plan on track and the scale will sort itself out. You can't control how much you weigh on a given day except by the choices you make - your period isn't a conscious choice, a second helping of dessert definitely is. Focus on behaviors and you WILL get to your goal, even with some weeks of no losses or gains along the way
Weight loss isn't linear. It's barely a downward trending scatter plot for some of us, unless we take a veeeeery long view of the data!