Supply regulating?

How soon can your supply regulate? 3.5 weeks in and I started noticing a couple days ago that my boobs aren’t that hard and don’t seem as full in between feedings. Where as before they’d be rock solid in between. My baby is still nursing great (20-25min a session every 2.5-3hrs) seems very satisfied and has plenty of wet/soiled diapers. I just don’t get if this is me regulating already or my supply is going down??