I don't think you can have water flavourings until week 3 but it might not be that. I find I can stay the same all week and then all of a sudden the day before my weigh in day it comes off. Stay off the scales until weigh in day-you might get a nice surprise. Good luck.
Maybe the flavoured water has slowed your time gettimg into ketosis, if i only have 2+litres per day my losses virtually stop. My body just needs more! Stick to it, it will happen xx