6weeks old doesn’t want to drink milk

Hello mommies, my LO is almost 6 weeks old, she drank 100ml per feeding up to last week, this week she doesn’t want to drink as much, we reduce to 80ml and sometimes she didn’t finished it either. She always falls asleep during feeding and got angry and cry if we keep feeding her. Today we fed her as usual but she only managed to drank 40ml and refused the rest. Anyone experienced the same problem and can share any advise? I’m so worried. Anyway she drink expressed breast milk. Thank you