I felt that way in my first pregnancy. They talk about post partum depression ad nauseum but never mention perinatal depression which affects 10% of women, apparently yourself and me included.
I'm also a teacher and remember that when my students were good i felt good about hte pregnancy and when they were bad I became worried that my kid would wind up like that too. I was very depressed.
There is therapy for perinatal depression and I believe even pills you can take that won't affect the fetus but I'm not sure. My depression did ebb by about 17 wks so I didn't go those routes, though if it happened to me again I would because that would've helped a lot.
As for your husband, I think that knowledge is power and the best help will be to share any knowledge you have about perinatal depression with him. If you read a pamphlet on it, give it to him, etc.
Good luck and congrats on your pregnancy!!!