Question for those that have ONLY breastfed (no pumping)

How did you notice that your supply was getting less? was it the frequent nursing or your LO being fussy..?

After nursing my daughter won't get fussy but will sometimes suck on her toys. when I see it I offer my breast again but she doesn't want it. Some evenings she wants to nurse every hour. Then there are times she doesn't want to nurse and I will get engorged. I tried to pump/hand express a little bit to see if she would take the bottle, but she mostly plays with the nipple and eventually the milk is gone.. but then she spits it up after a while.

I'm not sure what to think about it.🤔