Also late to this discussion, but wanted to reinforce Shannon and SK's comments- my two boys were in day care as infants ( both started part time at 3 months, then full time at 6 months), and I pumped at work too. With my first, I cried a little bit, but what felt worse was this big hole in my body left by my child while I was at work. It really felt like there was physical damage done to me. I was able to go and nurse my son over my lunch hour, which helped me so much. I got to be with him, he and I got to nurse, and i got to sit with the two amazing women that took care of him. That made my life at work even more stressful (I could drive to day care, nurse, drive back to work in just under an hour, so I ate a sandwich in the care- how relaxing), but also helped me stay connected to my son. I feel like I was very lucky to have a job that I really loved, and supportive people at work that were glad to see me back, and that helped too. And once I made some connections with some of the other parents at the day care, I really was able to feel good about our situation. Now that this baby is a five year old, I definitely see how he has benefited from day care. He has no problem with the basic social structures of taking turns, waiting in line, eating lunch with a group, sitting in his spot on the conversation mat, etc, etc.
The big thing with all of that is that you have to trust yourself and the situation that it's going to work out with benefits. So if you don't feel that way, then as others have talked about in their situations, then maybe having your child in day care isn't the right choice for you and your family.
I'm glad you're reaching out and talking about how you're feeling. This is why it truly does take a village!