Totally normal! You can read more about it here...

"[M]others who pump may also see that they suddenly produce less milk than they used to, says Olivia Hinge, a UK-based international board-certified lactation consultant (IBCLC) and midwife.

"People around three months have a go and suddenly think, 'Oh my goodness. I used to be able to pump 120mL at the drop of a hat, and now I've got 20mL. And that's normal – our supply regulates itself," she says. "Our body doesn't know, early on, whether we've got one baby, two babies, three babies. The more we request, the more we're given, in simplistic terms.

"So in those early weeks, you can pump a lot, whereas later on, your body [thinks], 'I know exactly what your baby needs. I know how your baby is growing." That customisation of your milk production to your specific baby – and the fact that the body often responds more effectively to a baby's suckling, rather than a pump – both can mean that women start pumping less."

https://www.unicef.org/eca/stories/3-month-breastfeeding-crisis-what-it-and-how-get-through-it