Aww hun, that's exactly how I felt after my STS on Monday. Crap isn't it? :bighug:
But...don't give up. You have come so far, and lost so much. I know it's rubbish, to get an STS when you've tried so hard. But try and think of it this way: does it matter, really, in the long term grand scheme of things, if you don't reach that mini target by your holiday? Even if you STS between now and then, you are still almost 4 stone down! You are, and should, feel amazing anyway!!
Also, you've increased your exercise recently, did you know that if you work muscles beyond what they're normally used to they'll retain water until they recover? So you could have a hidden loss.
Go and look at some of your before photos, and remind yourself of how far you've come! And then take a deep breath, say you're not going to let an STS beat you, and carry on x