post-partum depression, for real?

People keep asking me what I'm depressed about. It's not ABOUT anything...it just IS. I don't know how else to explain it. It's a feeling of despair that just won't go away. I've been told by two different Psychiatrists that it's "post-partum depression". I don't know. I wish I could rewire my brain for happiness. I can be just fine one minute and the next the world overwhelms me and I just want to curl up in my bed and go to sleep. I have a very hard time sleeping at night...I know it will just lead to waking up and dealing with another day. Then when it comes time to wake up I have a very hard time dragging myself out of bed. I've been told that I do not have a "normal" threshold for stress. The littlest thing sends me into a panic attack. I don't know if it's more neurological or psychological, but I wish it would just go away so I could appreciate each new day that God gives me.