Not Producing Breast Milk

When I gave birth to my son six years ago, I had hard time breastfeeding him because I couldn't produce milk for him. We couldn't figured the reasons why. I did the best I could from eating a lot of soup to using a breast pump, but none of them worked. After few weeks of trying, we decided that he will have to be fed a milk formula. I just wished I've know some other ways or even tip on how to increase breast milk production. I was worried he would not get the vitamins and nutrients he needs to grow healthy, but I was wrong. He is now a healthy first grader who seldom get sick. He has seasonal allergy though. Thanks to the milk formula he had when he was a baby.