Constantly thinking about the circle of life...

I think I may have postpartum depression. After having my baby at 31 weeks and 5 days... I constantly think about how much time do I have left on this earth? this kid is going to get older... get married... maybe have her own kids... and I'm going to get older and older then my life will be over. It makes me so sad. I never realized what life was all about. now I do and it frightens me. my baby has been in the nicu for over a month. I've only held her 4 times. its been hard. but I try to smile everyday. I'm scared to bring her home. I feel like I know nothing. I feel like she doesn't even know me. anyone else going thru something similar?