Think about what you're doing when you weigh yourself. You are weighing all of you. Everything that's in you and on you. So when you eat food or drink liquid, the weight of it is part of YOU, until it's digested and excreted. And whatever you where gets weighed. As does whatever water you are retaining. And the weight of your muscle. And your hair. And your fat.
So, here you are trying to lose FAT, stuck with a tool that measures ALL of you!
There are tons of fluctuations. Some of us either don't mind them or learn to deal with them or are even interested in what makes the scale go up and down. Other people hate them or can't deal with them. How often you weigh will depend on how well you can deal with those fluctuations!
Regardless of whether we weigh many times a week or once a week or less, most of us choose to record our weight until circumstances that are as similar as possible. I record my Monday morning weight, after peeing, in underwear only, always on my bathroom scale. While this is still subject to some fluctuations, it's the best measure I have of my actual weight loss (or maintenance) over time!
So, get used to the fluctuations, cause they aren't going anywhere!!
My 5 C's of healthy living: Commitment to conscious control, with the understanding that choices have consequences