Here’s the deal. It takes 3500 calories of over-eating to gain a pound of actual stored adipose fat tissue. If you didn’t eat that much in the period you’re looking at:
1. Water weighs 8 1/3 pounds per gallon. Temporary weight gain from hydration differences is totally normal. If you’re a woman and it’s about your TOM, or if you’ve had a salt-filled day such that your body needs to retain some extra liquid to dilute that down, it’s going to go away in a couple of days.
2. Which brings to mind the longstanding advice to only consider your weight change on a weekly basis; scale-gazing can bring too much of a sense of today-change vs. life -change.