Is it okay for weight to change every day by a lb?

sometimes I gain a lb but I don't eat very much and then I lose it, and gain it again, what the heck is going on? Is this normal? Every day its going on like this.Is it okay for weight to change every day by a lb?Are you weighing yourself at the same time every day? You should only weigh yourself once, first thing in the morning. The fluctuation could be explained by water weight.