The number you see on your scale can vary up to 4 pounds from one day to the next without you losing or gaining any weight!
These are simply fluctuations related with how full or empty your stomach is, your level of hydration and many other factors.
What to do?
Well, don't draw conclusions on these short term variations. They don't tell you anything about what really goes on.
The number you see on your scale is just one indication and the best is to check long term changes rather that these daily short term fluctuations.