Somewhere around 4-6 weeks postpartum (potentially as late as 12 weeks), your milk supply will begin adjusting to meet your baby's needs. How much milk you will make at this point will be determined by the information your body gathered during the previous weeks of breastfeeding. If you nursed or pumped infrequently in those early weeks, your milk production may decrease at this point because there were not enough "milk-making factories" created to match your baby's needs. Essentially, your rate of milk production will go up or down based on how much and how often milk is removed from your breasts. Some signs that your supply has regulated are: you lose that feeling of fullness in your breasts, and they may feel soft or even empty — your breasts are never truly empty, though! "Empty" breasts are working breasts.
You may stop leaking and feeling let-downs (or feel them but not with the same intensity as before), and if you pump, you may notice that you're not getting as much milk. This typically doesn't mean you're not making enough for your baby, but if you have any concerns, a visit with a lactation professional can ease any concerns.