I see a counselor. It's their job to diagnose whether you have a problem or not. If you feel you need help, especially if you're thinking if suicide, go talk to someone.
I've had three counselors though. First one I just didn't click with, and the second one I found out too often diagnoses her patients as being bipolar. Which she did to me. I didn't like hearing that most her her patients "were bipolar", so I switched again. My current counselor just said I have very deep depression and some anxiety.
If you find you have depression, have loved ones look after you after the baby. You could get PPD.
I feel the same way, constantly bitching at my hubby because I'm depressed. Don't worry, I'm sure you'll get passed passed he depression. That's what everyone is telling me, If it continues I'd consider seeing a therapist or talking to someone who's been through it before. Stay strong. :)