Try to check her nostrils, the same exact thing happened to me three days ago at 1 day 2 days short of week 5. See if there’s anything blocking (like nose s***) Mine was because of it, he couldn’t breathe so he got damn annoyed at drinking milk he drank like 20-30ml per feed. From 850-1litre of milk plus latching to like 500ml without latching. My baby was 5.5kg on that day and his usual feed is 100ml. He was like that the whole entire day and half the next day when we finally removed his nose s***, it got better, drinking 80-90ml after that.
my baby is 1 months plus. she is a sleeping beauty. daytime, sleep every 2-3 hrs and she would sleep 4-5 hrs straight especially at night. her milk intake is 60-90ml. her urine is good. her poop is once every 2 days. she is on mix feeding. PD says her weight gain is normal range. nothing to worry much.