Feeling Down

I’m new to this and joined for some support groups. My baby is home after almost a week in NICU and I’m still feeling sad and down. I comes in waves but mainly hits me around 5pm. This is my 4th child and I never went thru any postpartum depression with my other 3. So this is new and idk what to do. I don’t feel like doing anything(i do still get up and nurse/take care of baby), I feel like I’m not where I need to be as a mother of 4 and feel hopeless that things will change, I wanna go into a cave and cry a lot and just stare and be alone. Is all this normal? What can I do to help? I’m tired of crying and being sad but can’t seem to shake this feeling.