Breastfeeding

Hi mummies! I am currently 7 weeks pp. My supply has been low from the begining, only yielding about 60mls each pump. These few days I notice my supply is dropping to only about 20mls now. I have been drinking lots of fluid , water, barley, red dates tea, milo, oats and also eating nutritious food throughout the day. But still no improvement. My LO only wants to drink breastmilk and is rejecting FM when I try to top up. I feel very heartbroken everytime she struggles and cries. Sometimes feel like giving up breastfeeding and giving her full FM. Feel horrible that I cant satisfy her hunger. :'( Is there any hope at all to increase my supply? Any idea why this sudden drop?