Hi Wockets, and welcome to the forums!
Your story sounds a lot like mine, I was prone to bursts of motivation and I'd always be really strict for about 3 months, and then just end up getting frustrated and giving up when I had a slip up. Now I'm beginning to realise it's not about being perfect, it's about trying to do your best and then moving on when you have a slip up. Good luck with the weight loss!
Oh, and don't leave it until New Years, start today!