Post Natal Depression While Pregnant?

Well I guess it's not true post natal since I'm pregnant again. I have a 7 month old daughter and am expecting my son in October.Lately I've been really,really down.This pregnancy is nothing like my last.I felt awesome with my first pregnancy.This pregnancy I feel awful,apart from having every single pregnancy symptom possible, I just feel run down and crappy. My husband is really getting on my nerves lately. He comes home from work and figures his day is done. I have to ask him to do every little thing when it comes to caring for OUR daughter and then I feel like a nag. I'm excited to be having a boy, my family will be complete but I am dreading it too. If my hubby is this useless now how will it be when I have the next baby.That gets me really down knowing that if I think it's hard now,well just wait for the next one to come! All this is really getting to me and it's affecting my life profoundly. I don't feel very happy most days. What should I do? I am wary of taking antidepressants