You aren't guaranteed to get PPD but you have a higher risk...especially if your pre-existing depression is not being controlled....I have depression, i've never had ppd.... Matter of fact my kids are the one thing that keep me from getting too depressed....when i start to feel bad i think about what my kids would go through if they lost me and it pretty well helps me to snap right back.
I like Linzola's answer. But you're definitely in a position to have a higher chance of having PPD.
It depends honestly. I was diagnosed with depression when I was a bit younger and have had moments when I was depressed and times where I wasnt... When I had my son the week or two following were hard but that time peroid is called Baby Blues!!!
Just because you are depressed it doesnt mean you will have postpartum.... You may have a few weeks of hard time but you may also find the baby helps with your depression!
Yes a history of depression will increase your chances. Your OB will usually ask you if you have a history of depression.