We seem to have opposite problems -- I tend to loose too much while fasting. Only if we could exchange part of our tendencies ... of course this is not possible.
I have two guesses: 1. Could you be using different scales, which would have given different measurements, even if used at the same point of time? Do you always remove your shoes, belt, keys, heavy cloths when weighing?
2. Could it be there hardened tissues/substances/inflammation that now have the chance to take in water and slowly work toward dissipation, but keeping your weight from dropping for now?