3 pounds is a perfectly standard order of magnitude for the natural daily oscillations of our body. It can be from water (under many different forms: stomach, bladder, intestines, glycogen water, morning dehydration, post-workout dehydration, ... ) or from food being digested at various stages (and glycogen).
You should not see that as a significant difference. And the fact that there's only one day between your two measurements is yet another indication that this is just part of this natural oscillation rather than anything significant. Only look at the "mobile average" curve of your weight smooth down on a one week scale.