I know with me there's a load of other issues, but losing weight gets harder as you get older!!! How middle-aged do I sound? But it's true...I have a WAY harder time losing weight now than I did when I was 16, 17.
It could just be that that's changed...or a combination of that and no smoking (yay for you, btw! ).
I think that if you don't worry about watching calories too much and just avoid sweet treats, and carry on exercising like you are (and don't watch the scales too much), you'll start losing after a few weeks. It takes time. Boring!