for starters, unless you weigh over 500lbs you shouldn't be losing 5lbs per week [which is what 15lbs in the 3 weeks between your periods would be]. that sort of loss isn't really sustainable for smaller people. there is a little wiggle room when you're just starting out, but you can't expect to see those kinds of number all the time. quite frankly it looks like you may have started weighing in before you lost the last of the retained water from your last period, which if you're gaining and losing about 7lbs with that, would put you at losing just over 2lbs per week, which is reasonable if you're a little over 200lbs.
secondly, some women have periods that have big impacts on their weight. you'll need a few months of periods to full see exactly where you are on this spectrum, but some women who find that have this issue don't weigh in the week of their period so they don't have to see and freak out about the gain that goes away the next week. part of your problem is that if you're eating whatever you want, it's likely processed which means that instead of just having the additional water weight from you're period you're adding in a ton of extra sodium [more water] and are likely eating more carbs [more water again] which means that what you're eating is roughly tripling the amount of water you're retaining during and around this time.
if you are lazy during that week, make it your goal to spend the other three weeks of the month cooking for that lazy week. so when you make a pan of lasagna on a not period week, make an extra portion or two to freeze so that all you have to do is heat and eat come period week. do the same for soups, stews, anything that freezes well [test freeze a few ounces if you are not sure if it will work and reheat well] so that all you have to do when you're lazy is grab, heat and eat.
you may also want to reset your ranges to maintenance ranges for that period week. it will give you more calories to work with during that week, and while it will theoretically make your total loss slower, it may make it shorter because you wouldn't be overeating to gain during that off week and cancelling out some of the weeks of eating in your loss ranges.
-google first. ask questions later.