Don't get too caught up on the numbers tha scales show. Sadly there's a huge number of variables to take into account - Don't just think that because you've weighed yourself and the scales are showing you 3lbs heavier than 3 days ago that it means you've gained 3lbs in 3 days... so many things can alter the reading!
As steve says, were you wearing anying different to when you last weighed yourself (ideally you shold be weighing yourself whilst nude anyway). Have you been/not been to the toilet (number one or two) before weighing yourself today or three days ago. When was your last meal? What time of the day did you weigh yourself at last time? Are the scales in the same position on the same surface as last time? Are your scales accurate in the first place?
I use some cheap digital scales, and weighed myself on someone elses scales and their scales weighed me 1st lighter! I felt I had to burst their bubble and tell them their scales were wrong (I'd checked mine, weighing 20kg of weights at 20.01kg). I also weighed myself the other night, putting the scales on the carpet (usually weigh myself in the bathroom) and was a little annoyed to see an increase in weight - then I put the scales back in the bathroom and miraculously lost 3lbs in approx 5 seconds!
Anyway, I'll stop waffling, but in response to your post... perhaps keep a log of your weight each time you weigh, so you can see what's happening long term - and also make every effort to weigh yourself in the same circumstances each time!
