Low milk supply

My baby was diagnosed with Galactosemia Duarte. Which is one of the newborn screening they do at time of birth. What is it is that she can’t have lactose because the sugar in the milk is bad for her. Long story short they but her on soy milk and I stop breastfeeding completely. Two day ago she had a follow up appointment and after a month of strict soy milk she can go back to breastmilk. The problem is that I am not producing enough milk for her. Any suggestions on what to do to increase my milk?