Please help =***(

So, i had really considered myself to know quite a bit about breastfeeding, i had nursed my now 2 year old all her life and now new baby is here 10 days old born at 37wks and having issues with weight gain. We had another weight check today she only gained one oz. Originally was 7.5 then 6.10 Thursday and now today only 6.11. Doctor is already saying to supplement which i really really do not want to do is there anyone else going through this?