A.B.
M.,
I'm sorry you're struggling with this. The pp time is so hard.
In addition to the great advice you got below, I want to add that diet can be a huge factor in helping with this. Be sure to continue your prenatal vitamins and consider either supplementing or eating more foods rich in B vitamins and iron. Inadequate amounts of both of these have been linked to depression.
For me, exercise has also really been helpful in staving off depression at certain times of the month and during the pp recovery period. 30 minutes of aerobic activity has a comparable result as many low-level depression meds. You didn't mention how far pp you are, so be sure to get the dr's ok here.
Finally, you're going through so much. Do you have anyone to talk to? Anyone to lend you some support? Not to trivialize your situation AT ALL, but sometimes we're just not used to hormonal shifts and not feeling well, so we think something must be wrong with us. The truth is, there is such a wide range of "normal" when navigating these times. Be patient and forgiving of yourself. Feeling isolated at home w/a new baby can exacerbate feelings of loneliness, fear or inadequacy. This is also normal. Is there a church you can plug into? A MOPS group? It may really help to get out.
If you are attending to your needs for fresh air, exercise, these essential nutrients and you're still not feeling well, or if at any time you have feelings of causing harm to yourself or your baby, definitely move forward with seeking help.
Does your hospital employ nurse-midwives? They can be wonderful resources as they are committed to treating all of you: physically, emotionally, etc. A post-partum doula might also be a great place to start. Here's something for your area: http://nycdoulacollective.com/
I'm sorry I ventured a bit outside of your original question, but I found this info helpful when dealing with extreme hormonal shifts due to pp and PMDD. I wish you the best.