I hate to say it, but you shouldn't be worrying too much about weight loss while feeding a baby so young. Once he is onto some other solids, in a couple of months, you can think about restricting your intake, but right now, you are it
for his nourishment and shouldn't jepardize that in any way.
That being said, you can still help yourself to lose a bit of weight by avoiding all junk calories (cookies, chips, candy, deep-fried fast foods, etc) and eat only the best, most nourishing foods when you do eat. And drink tons - that's one of the main factors in making enough milk. Other than milk, if you choose calorie free drinks for most of your beverages (avoid sodas and real or fake juices), you will reduce your calories that way, too. Also, getting some gentle exercise, like taking him for long walks, will help with getting the muscles working and burning long, slow aerobic-type calories.
Congrats on your new son! I have 2 boys, now teens, but I remember the joys of the baby stage.