How much should weight fluctuate daily?

It could be a number of factors, including the precision of your scale and the time of day which you weigh yourself. Whether or not you've just eaten or used the bathroom will influence your weight. A liter of water weighs 2.2 pounds, so you can see that a meal can increase your weight by a few pounds, at least temporarily. Try to weigh yourself at roughly the same time during the day to minimize variability. Understand that your weight will naturally fluctuate from day to day and that you should be concerned with meaningful trends in your weight over time that are greater than this 3-5 pound range.