Depression

I know there is pp depression, but is it possible to, randomly, develope depression in early pregnancy. Im only almost 6 weeks along and im constantly depressed, anxious, and irritable. I wake up in the middle of the night and cry, i start crying in the middle of the day. I never really have a reason. Just that i feel sad. Ive never been like this in my life, or with my other 3 pregnancies. Its starting to take a toll on my marriage and im really questioning if i can do this for nine more months. Anybody else experience this?