hi. my 15 day old girl used to drink 80ml ebm every 3 hrs. as my supply is not enough, I started giving her fm (nan h.a.) for night feeding yesterday. but both feeding she took only 30ml. I changed to ebm and she took 70ml. but this morning, she took only 40ml ebm again. is this a cause of concern?

Fm is more filling than ebm as ebm is easily digested by the baby. Hence you may need to give more ebm than fm. Your baby is still young so it's probably normal that the volume intake varies. The intake may stabilise (or increase) as baby gets older. As long as baby is peeing and pooing, 6-8 dirty diapers a day, it should be ok.