Thats great weight loss, some weeks will be lower than others. The girl in the chemist told me drink at least 4 liters of water but don't go over the 4 liters as your kindneys won't cope. I was a bit down last week with a weight loss of 3.5 but this week it was 5+3/4. So hang in there and drink lots ;-)your doing great.
I think your weight loss is exceptional for the first two weeks given that most people your height would take four to six weeks to lose that amount.
Your weight loss will probably settle into a pattern from here on as your glycogen stores would be now empty and I think if you can achieve anything from 2lb, 3lb or 4lb every week you would be doing really well, anything more would be a bonus.