Haven't read most of the thread but what Dave said is pretty much spot on. Will give a couple of alternative options though...
Diet drinks have something like 3 calories per can, "full fat" are about 150.
If you are going to drink try and stay off the beer, vodka and a diet coke/lemonade will be a lot better for you calorie wise.
Not sure if its true but green tea is supposed to speed up your metabolism.
Try and do as much exercise as you can, even if its just running up and down the stairs a few times. As others have said walk the walkable distances, its all too easy to jump in the car for something that will take you 30 mins to walk.
Not sure if you are a fan of lettuce but I have found the more you eat it the more enjoyable it becomes.
I have replaced my brunch time crisps with a snack-a-jacks (one of the big ones, they are about 42/46 calories each) it is about a third of the calories of a standard packet of crisps, even half the calories of the "good" crisps like french fries or quavers.
Have a look at some of the stuff you eat, its amazing how many calories are in certain things if you have never really taken an interest before even in things you have previously considered good.
It will probably take longer for you to notice a difference but it really does give you a boost when people around you comment about how much weight you have lost.
Not great advice, I tend to ramble on a bit at times

Good luck
