Well, what has been going on in those 3 days?
Food intake? Workouts? Time of the month? Water intake?
Can be hormone related, too much salt, too little fluid, too much food, increased water intake, constipation, more working out, less working out, less caffeine (diuretic), etc etc .....
Did you weigh yourself at the same time everyday?
THIS is why weighing yourself everyday is silly. Too many variables impact weight. Weight alone is a meaningless number.