Does she take full feedings when she does wake in the night? If so, it's possible she is hungry & I would look at her eating during the day. When she nurses in the day do you feel the milk let down or notice a difference in how your breasts feel after she eats? How much is she eating for solids? If she's not taking full feedings in the night, it may be that something else is waking her & she's not going back to sleep on her own, separation anxiety kicking in, or other developmental issues.
I hope things get better soon - I know it's hard to not know & to question your supply!!