I had this today too actually - I'm trying to be in a size smaller jeans each month & November's NO WAY do up yet. Which wouldn't matter (over a fortnight to go & who cares anyway?) but my mum's coming to stay next week & she's the queen of the 'how's the diet going dear?' raised eyebrow routine! So I threw them across the bedroom & generally sulked a bit...
...& then decided (as people have said) to focus on what I HAVE lost (ie slightly slimmer now than pre-pregnancy). Cheered me up no end.
I actually find the jeans thing is working a bit tho'...(admittedly boring) jeans from Evans are only £15/20 & I feel I've achieved something when I zip up a new pair & chuck another 'baggy' pair into the charity shop bag. & I jolly well WILL be in those size 18s by 1st of November!
OK, not as much fun as a whole new skinny wardrobe, but if you're losing weight & want to mark off the stages w/out blowing the budget on 'interim' clothes I can definitely recommend it - not necessarily jeans, but anything cheap'n'cheerful that makes you think 'wahey, that's another 2" off all round!'