0.5? that's nothing. I dump more than that
You need to stop fretting about the little things like that.
I can and do vary 3kg depending in the time of day, you will even more so (you have an ewwww week which will cause a pretty irregular weight)
Fitness challenge, make a body comp change in the next 6 weeks (loose fat or gain muscle) and don't use a scale for whole thing. It will be the best thing you've ever done, you'll learn to use mirror tests, progress photo's etc and not rely on a flawed measure