Is depression BEFORE birth normal?

I've heard of post partum depression but lately it feels as if I'm already getting it.. My babies father is such an asshole and changes his mind about being a dad every other week, and it breaks my heart knowing she probably won't have a full time dad. Not to mention how in love I was with him before I got pregnant and he left.. It feels like my insides are being ripped out and I don't wanna leave my room ever. I'm worried I'm putting the baby under stress and should maybe get some help but I'm not sure what there is to do, I can't take medication because I'm pregnant. Is depression common? What would you ladies suggest? I'm so heartbroken.