Hi Jools
Everyone is different and different things motivate us. For me it's a stages thing.
I just need to have 1 day of being good - that first day, which is always the hardest, but the next day I wake up I feel so proud of myself and happy that it really motivates me to do the next day.
Saying no to something (like the gorgously yummy chocolate biscuits that someone's bought into my work and are within a grabbing distance to me) once, makes it so much easier to keep saying no.
So for me it's never like I have to be good on my diet until X ... it's just be good today, or even just say no at this moment and deal with the next when it happens.
It works for me ... well most of the time anyway lol
You can do it, I know you can - it sometimes just takes a while to hit that zone ... but when you do you'll wonder why you ever struggled before!
Good luck!
xx