Sometimes postpartum depression can turn into a long term situation, whether it be anxiety, depression, bipolar disorder, personality disorders, etc. I experienced postpartum depression with both of my children, my oldest is now 4, and my baby is 1. After the birth of the first, it never went away, and it continues today but has manifested itself as bipolar type II and was brought on by the depression. :(
It could be hormones, it could be a ot of things. Relax, make a doctor appointment. They will ask you lots of questions and do some blood work to see if anything is abnormal in the blood and go from there. Relax, motherhood is stressful, but call your doctor.