Good night I'm experiencing something like I've torn off a part of mys…

Good night I'm experiencing something like I've torn off a part of myself, there's very little breast milk, I've tried everything, only feeds on breast milk in the morning, and that's it, I have to give formula, but when I give formula my eyes fill with tears as if I'm a bad mother and can't breastfeed, like I've torn off a part of myself. Another question, I fed NAN, decided to switch to Nestogen, it regurgitates after every feeding, is this not suitable for formula? Or will it get used to it?