How to increase my milk supply?

smiley

My twins are 1 month old and they still not latching on the breast. I used to pump for them and supplement with formula as needed. Now with my husband back to work. I ending up given them formula for 2 weeks now because I was too tired to pump. I wanna try breastfeeding them again with the nipple shield. However my milk is drying up. What can I do to increase my milk supply?