How long have you been doing sw and how much have you lost/gained?
I had a 'wobble' over the last few days but think i'm back on track today and i have started either ww or sw more times than i can possibly remember so i know it is really hard if your head's not in it. I know it sounds simple but write a list of why you want to do this and hopefully it will inspire you! I also just look at an awful photo of me taken at xmas and it makes me determined to lose it for good this time.
Don't be so down on yourself, i bet most people on here know exactly how you feel and have been there themselves x