It is perfectly normal for weight to fluctuate day-to-day, largely in response to fluid shifts. But if those unexplained changes frustrate you, then don’t weigh yourself every day.  Once a week, twice a month, or once a month is enough to monitor trends, especially considering that weight control is a lifelong activity.  When you do weigh-in, weigh yourself upon arising, wearing light or no clothing, after emptying your bladder, and then record your weight immediately!  Also track other indicators of progress, such as your measurements, the fit of your clothes, and your fat-to-muscle ratio.  Daily, focus on those things that are under your direct control:logging your food and activity, eating a balanced diet, getting your exercise, and performing the other goals you set for yourself.