It is almost impossible to lose a pound of fat in 24 hours so it is most likely fluid. Are you drinking enough water? Are you watching your sodium, especially during your late night snacking? Cheese, cottage cheese, crackers, sandwich meats and things like that are usually very high in sodium. I don't know if you eat those things. If you prepared some cut up veggies and some zero point dip would you eat that at night? Could you stop stocking whatever it is that you always snack on for a while?