I wouldn't worry about it. There's a reason it's good to weigh yourself only once a week
Our bodies can hold a lot of extra water. As it's only your 3rd day, and your body has this big change happening and has to adjust to it, I really wouldn't think anything of it.
If you're on (or close to) your TOM that can be a big thing too....I know the week of mine, I tend to hold A LOT of extra water, but it all goes away the following week.
Don't be discouraged! You've been on this journey before, so you know it works
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