It's amazing how many calories you can consume without even thinking about it.  Once you make yourself conscious of the calorie intake it makes things simplier.
There's a site online 
http://www.fitday.com/ where you can keep track of the calories.  It includes info on how many calories you burn based on your lifestyle, age, height, weight, etc.  So if for example, on a typical day you burn approximately 3,500 calories.  Drop your intake to 2,000 calories a day and you can lose 3 lbs a week.