I have to say with my 3.5kg, that my week 2 weigh-in was a bit of an anomaly! I put in the body of the email, but guessing it didn't get read!
week 1- 80kg
week 2- 82kg
week 3- 78.5kg
Week 2 was weighed in the evening after a day at work and meal etc, whereas the other two were near enough first thing in the morning! Same set of scales etc. however so should be the same inaccuracies.
I'd love to know how much I really lost over the past week; I had a week off work and had been squirrelling away at my university project work- meaning not much exercise and barely any sleep, but plenty of caffeine and a few missed meals! I expect the weight will go straight back on as soon as I get into a more normal routine again 🙁