PPD... how do you know?

I sit in the NICU, right by my baby's side every day, and I feel this overwhelming sensation run through my body, I don't know how to explain it but I just want to scream and cry. I feel so helpless and useless while my baby lays in the incubator. I try to keep myself occupied by reading, Facebook and other little things but it always comes back to me feeling empty inside. This is my miracle baby, my first one. So regardless of how I feel I'm going to be here with him. I'm just wondering if I should talk to someone. Or if I do talk to someone, am I going to be able to open up and tell them how I really feel...