why does my baby eat 1-2oz every 4 hours

my baby is 6 weeks and two days old. sometimes she finishes 4 oz bottles but she usually eats 1 and a half to two and falls back asleep for 4 more hours. pediatrician said she should be eating 4-5 oz every feeding rn. my baby was born 10 pounds 7 oz and took a month to get back to newborn weight. why would she be eating so little but sleeping so much? is she eating enough? this has been going on since birth basically. and yes ive tried tickling her feet , keeping her up, wet rag on face changing diaper, changing rooms. stroking cheek, blowing on face, playing baby music and nothing will keep her awake. shes a heavy sleeper. im formula feeding bc i only make about 1 mil of breastmilk so i take supplements and am working on increasing supply, i pump and give her what i can thru syringe (1 mil or

less) but i also have thyroid disease so that could cause breastfeeding issues (even though its controlled) anyways off topic. is it normal for her to eat so little and sleep so much? i dont have a current weight because her 2 month appt is in oct. last weight at pediatrician was 10 lbs 5 oz on sept 11th