I suffered from horrible depression while pregnant with my last baby. Its so hard to deal with. Part of you feels guilty for being depressed, which only makes it worse. Its nothing you can control though, if it is truly depression. Its hormones. It has happened in two of my 7 pregnancies. I was advised to go on medication but refused because I was too worried about the baby.The good news is that it just goes away eventually. At least it did for me. And I have NEVER had postpartum depression----only IN pregnancies, twice.
I would be depressed too if my husband was gone, so I can understand where you are coming from. You need to find someone to talk to. If talking it out doesn't help, see your DR. for advice on whether its true depression.
I am sorry you are going through this sweetie!
Jenny gave you some great advise.
One thing to note is that depression is depression - it doesnt matter WHY you are depressed because the end effect is the same. Definitely talk to your doctor about it and they can determine how bad it is and what the best course of action is. If the depression is bad enough it can effect the pregnancy (premature birth etc.) but there are many good, safe, treatment options IF this is something that doesnt pass on its own.