Pumping mamas

I need some info because I for the life of me cannot remember how pumping was for me in the beginning with my last pregnancy. My baby is in the nicu so I had to pump for him. He is not able to bf at the moment until he improves. My milk came in full swing almost too quickly. So at this point I am pumping and getting about 8 oz in a session. 6 if I am pumping about 3-4 hours on the dot. What I notice though is my boobs are still heavy and big af even after emptying 8 oz. is it just from my boobs being swollen from milk coming in? I can’t remember if my boobs felt this heavy after pumping in the beginning.