OK, so this is obvious and simple.. but maybe someone hadn't thought of it this way... so here goes!
I'm a long time lurker that joined last night.. and whilst lurking i've seen a lot of threads with people that are so close to target (or didn't have loads to lose from the start) that are downhearted with their small losses. Other people.. like me, at 18 stone, are seeing consistent 2lb's a week.. whilst you may only be losing 0.5-1lb.
Whilst number crunching, I realised something. At 18 stone, I need to lose a much higher amount to achieve the same percentage of weight loss as you. So, your 1.7lb's loss is equal to my 2.5lbs (ish) loss in terms of percentage of weight lost.
Hope that makes sense and spurs you on!