It does go up and down Rowantree, but 1.8kgs is a very good starting loss! Make sure you're drinking plenty and eating all the syns you are allowed. I think it's tempting to cut down on them because you think you will loose weight more quickly, but SW doesn't work like that.
If you are on Facebook, there's a very good group on there called 'How Many Syns??' and it's full of ideas in what you can eat, and if you're not sure, then post a query and someone will answer.
Keep going, and don't give up. I'm working on 0.75Kg/week loss - which is a reasonable loss rate and is achieveable. Don't look at the ones who say 'I lost 10lbs this week' - quickly off is quickly on again, I think. At 0.75Kg/week, by the end of the year I will be at my target weight - and I've got a lot to lose!