I echo what Stellarose said. Sometimes there is just no good reason. But you CAN turn it around. I had a minor carb fest yesterday and ended my day with a hard cardio session and a light dinner. I think I thwarted the potential gain. I also watch my sodium as she said. And drink that water!
I do know that weighing daily can be very helpful to a lot of people. I know that if I don't weigh daily I will eventually begin to avoid the scale- especially after a bad day. A lot of our maintainers are daily weighers
For some folks it's just part of the daily routine, like brushing their teeth.