Originally Posted by popspry
I did eat some salt-heavy foods yesterday. The only other difference is I was more physically active yesterday (not a ton more, but some).
Both of these things can cause daily fluctuations. Just the fact that your body is not a clockwork weight-loss robot also causes fluctuations. Everything from the volume of the food you eat and fluid you drink (some of which is still inside you), to the weather, to sodium intake, to recovery from exercise, to a host of other factors outside your control, can cause a fluctuation of a couple of pounds over the course of the day.
Please don't be frustrated by this. It is just how bodies are - you most likely cannot control it. You can either weigh every day and accept that fluctuations are part of the process, or weigh less frequently so you don't see them as much - those are your choices.
Keep in mind that what matters is not whether you weigh less today than you did yesterday (because chances are you don't, not in a measurable or meaningful way). It's not even whether you weigh less today than you did a week ago, because these natural fluctuations easily mask a week or two's worth of fat loss. What matters is whether you weigh less than you did a month or two ago - that is the only meaningful way to measure the success of your plan.
Stick with your plan; over time, the losses will follow.