weight loss and stopping smoking

I have lost 3 stone 8lbs in a year on mfp, so last month decided to give up smoking, ....but my weight has fluctuated since then and im actually 3lbs heavier this week.
My diets exactly the same, no hidden snacks or treats iv not logged....I use an e cig which stops me from reaching for the biscuit tin.
I read that once u stop smoking your body starts working more efficiently so burns less calories....around 200 a day.
I wondered if anyone has experience of this and if the change in metabolism is temporary and will balance out again?
I still have around 18lbs to lose and feeling very demotivated...
Im well atuned to my weights fluctuations having already been doing this a year and the only thing thats changed is that iv stopped smoking.