You're not on your own. I think it's something to do with setting a target weight. I was so near target two years ago I could smell it. Things got in the way and I put one and a half stone back on. Looking back I often wonder what I could have done differently. What I do now is focus on small losses each week and keep my eye on what I have achieved so far to motivate me. To lose nearly 5 st. is amazing so don't ever forget that. You can't be perfect all the time!
What works for me is to have a slimming buddy to egg me on. I am 12/9 with a target of 11st. I always feel accountable to someone other than myself then. Similar to a SW group I imagine. I have just done Kay's salad challenge on another thread and lost 5.5lbs in two weeks. Unheard of for me! Might be worth joining for a last minute push?
If you want a buddy - I'm up for it and have a lot to learn from a successful healthy eater like yourself