Definitely ask for help! You are not alone in suffering depression through pregnancy, and it can feel isolating if you try to work through it on your own.
Alice is right - online resources can help you with your emotions, and your GP or midwife will be perfectly placed to help you get back on track.
I got back on track quite quickly during my first pregnancy after talking talking it through with my husband and my midwife, and I have a friend who suffered (and survived!) quite severe antenatal depression. Whatever you are feeling, there are enough resources out there to get you through.