My recommendation would be to add some exercise -- even if it's 20 minutes of walking at lunchtime or after dinner -- and go from there. If I were in your position I'd keep a food/calorie and weight journal and see what patterns you can pick up from it. The most accurate way to know your calorie needs is to listen to your body. Over the course of a few weeks why not track your calorie intake and your weight -- the scale will tell you at least somewhat accurately what you're doing right (or wrong).