First off, I'm so sorry for your loss and that you have had to go through this. I could never imagine what you are and have been going through. However, you do need to try and be positive for the new child. Talk with your doctor, because they will know more on how to help you with the depression. Also maybe look into counseling, one that specializes in pregnancy and post natal. I saw a counselor while I was pregnant and still do, and I think it helps me. I wish you a safe and healthy pregnancy!
I'm so sorry for your tremendous loss. I had a late term miscarriage at 19 weeks and it was devastating, so I know the pain to an extent.
I agree with the above poster that you must seek professional help. You have to deal with the pain and loss and keep an eye on how you're feeling with the depression from the loss of your child, coupled with the hormonal changes that come with pregnancy.
There are many options to treat depression, because yours seems to be mostly related to your great loss (understandably), I think therapy and some kind of loss support group would be very helpful to you.
Keep us updated on how you're doing, and the very best to you.