Hey Charliebear, I've been in the same situation as you, and my diet would always start tomorrow, and come March, I'd had enough of putting on weight and feeling out of control. What I did was join this board, and put myself on a sensible eating plan rather than any diet, and I've just taken one day at a time.
For example, I've cut out snacking in-between meals, and if I am hungry, I'll have a piece of fruit (lower in a calories and much better for my body - BONUS), I've cut out naughty foods except for the day I weigh myself, and I've tried to do some exercise almost every day, even if it's just going for a little walk or doing crunches at bed time.
Key message though is taking it one day at a time, and infact even break it down to one hour at a time.
I also built myself a little network of friends who can support me during low times. SO if I desperate fancy some chocolate, I would call/email/messenger one of them and they would talk me out of it.
I hope this helps, good luck
