Decrease in baby’s appetite

Hello! My little one is 5weeks and she has been taking in much lesser milk this week. She used to take in 900ml to 1 litre of breastmilk per day. Since this week she has been sleeping a lot more too. she can even sleep through the night yesterday (slept at 11pm and we woke her up at 6am to feed her cuz we were worried she isnt eating as much). Any idea why is this happening? Her weight was 4.35kg four days ago and today she is 4.25kg.. Not sure if i should be bringing her to see a PD or to continue monitoring? Signing off, a worried mummy.