Not Breastfeeding

I’m not planning on breast-feeding. Due to medications I have to be back on as soon as the baby is born, and my own mental health, I’m not planning on breast-feeding.

What happens to my body when I don’t breast-feed? I’m assuming the milk will come in, but will it leak? Will I have to express it because it will become too painful? I’m a first time mom and don’t know what to expect.