Breast milk help!

With my first kid I was easily producing enough for her from the start even though I had her early. With my newborn now I could feel I didn’t have enough milk even at being 40 weeks. Now I am struggling to produce enough. I am having her take both sides 10-15 minutes each, every 2 hours even in the middle of the night. I am now having to supplement, but was told by nurse to continue with breast first and then supplement. Can someone please help/ advise? How can I up my milk supply and why is this happening if it didn’t with my first?