I explain all of this in Step 2 in mastering the scale--please go rewatch that especially the water weight section--it is a thorough explanation of what is going on--most of fluctuation like that are water weight and you will be seeing that a lot.
A lot of time our weight strugglers mind EXPECTS to be rewarded for being GOOD with progress on the scale--we have to remind ourselves to LOOK AT THE DATA--how much should I have realistically released so far? If the scale is up--it usually is water retention! We are over 60% water! Just for now do your best to collect the data--the chart will show your progress over time and remind you even when you are up--the overall trend is going down. Remember loving scientist--not disappointed dieter.