It's soooo hard to break those old eating habits, but you can do it. Don't psych yourself out. Eat healthy foods(learn to enjoy them, nobody ever said you can't eat a spinach sandwich..lots of spinach leaves stacked high with spicy mustard on small whole wheat bagel, for example), keep track of your calories, exercise, drink lots of water. All these things we know to do, it's just getting started, surviving those first few weeks and than sticking to it becomes a little easier when you start to lose weight. You can calculate how many calories you need at http://www.bmi-calculator.net/bmr-calculator/

I feel for you..Pizza is one of my biggest weaknesses..