There is a reflex, milk let down reflex in which when the baby suck the nipple then only  milk will release  from the breast alveoli. So your main function is first press the breast and  check the milk is coming from small holes in nipple or not. If no flow then consult a Sr gynaecologist. You apply sugar water on nipple and try to put your baby on breast to suck.  Every 1/2hrly.,drink milk three times a day. And drink water when you feed the baby.

It's better if you see lactational specialist or gynaecologist personally.  As there are several causes like stress lack of hormone, anxiety, nutritional deficiencies.