How many calories should you eat per day to lose 20 lbs in 4 months if you are 5'4 and 170 lbs and nursing?

Best to eat a very balanced diet...you need the nutrients in all different foods when you are eating for two. Watch portion sizes and see that you get 30 to 60 minutes of exercise daily. Sometimes with the hormone shifts of pregnancy, it just takes awhile for the weight to shift. Meanwhile, you can avoid making things "worse." Probably 1200-1500 calories including 3 oz protein per meal would come close. Avoid fruit juices with sugar, high glycemic carbohydrates (white bread, cookies, and so on). There is good info on the diabetic diet which will work wonderfully for you--not as extreme as Adkins or others and so not as hard on your system.