That sounds about right to me. I am also nursing and shoot for 2000 a day. I lose about (on average) a pound a week.
I shoot for more burn than restriction. I shoot to burn 300-400 daily with exercise. A brisk walk with some running sprinkled in burns about 10 calories per minute for me. If I eat some things that are a little higher in calories, I try to exercise them off rather than restrict more the next day.
If you are interested in more of the mathematical equation, you can figure your Basal Metabolic Rate. That will help you understand how many calories you need just to live and breathe (plus 500 for baby). My BMR is 1600, my baby is on solids now (7mo old) so I added just 400 for him to come to my 2000. Starting in January, I will be reducing my needs by 100 per month to arrive at 1600 when he is weaned at around a year old.
Here's the site I like for calculating BMR: