What sucks about going back to work that I didn’t know

FTM, and I went back to work after a year off. Before I left I would have girl nights with my co workers and felt that I had some real good girlfriends. But then I had my baby, and suddenly I was left out in the dark. I wasn’t invited to things anymore and I barely heard from my co workers except on Snapchat occasionally. Then I came back to work and while it’s obvious that I was put in a “mom” box by them while I was off I thought things would be better. After all I was “out of sight, out of mind” while off. But now after working with these people for a few years, suddenly I’m a kind shake this feeling of being an outsider and it just sucks. I feel replaced. And I feel left out. And I seem to have lost the people that I thought I could confide in. Maybe it’s just me, and maybe I’m being sensitive. But it sucks and it makes me incredibly sad at a place I once loved being at. And I just don’t know anyone else that gets it. Maybe I just needed to vent.