I'm worried about my sister but have nothing from my infant feeding experience to offer her. Her 5 week old feeds 2-3 times an hour during the day and every hour at night except once a night her husband gives the baby a bottle of formula and then she manages to get 3 hours of sleep. He is 1 lb over his birthweight. She's not in pain but absolutely exhausted.
My sister had Chemotherapy 5 years ago for cervical cancer. I don't know whether this could play a role.