Hormones or Depression?

This is my second pregnancy. With my first, I definitely remember some craziness and moodiness, but nothing to the extent that I'm feeling now. Of course I'm excited to be having another baby, but it just feels like I have nothing to look forward to, even though I know I do. I'm more likely to snap at the smallest things, which is not good because I have a 15 month old and I feel like such an awful mommy for not being as patient with her as I should. I don't know if I should chalk it up to being under a lot of stress, what with dealing with morning sickness, exhaustion, and having a toddler, or if it's a sign of something more serious. Is anyone else feeling like this??? 😫😢