7w Baby with runny/mucousy poop

Is anyone else experiencing this? my baby used to have curdled/mushy poop. now it's a darker mustard color and runny/mucous. He eats plenty, has the amount of diapers he should. He does get fussy at the breast sometimes. and he does it no matter what I eat, and will do it mostly at night, but sometimes in the morning too. His weight was at 80 percentile at birth, then in the 60 at 2-3 weeks, now in the 30. His Dr appt is the 23, should I try to get in sooner?