You may have it again since you are prone to it, but when you are a new mother and overwhelmed with the newness of your situation and trying to do be the perfect mom, it can get the better of you more than a second pregnancy. Granted, when you have a second child the the house, you have two little humans that demand your attention, but you've been through all the baby care stages before.
I believe that one of the main causes of post-partum depression is just lack of sleep.
I'm not saying that it won't come back, and I'm not saying that it can't be worse or better for you personally. From my own experience, the second time around was easier because of the "been there and done that". With each of my children my symptoms of depression have lessened....and believe me, having the children play together when they are a little older is a great load off your shoulders......do don't have to be your only child's playmate and mother too.
There are medications that are safe for pregnancy and post-partum. Your doctor should know which one is best for you. But I do think that you will do better if you choose to try for another child. Just don't worry about what others may think and remember that you are doing the best you can and that's all that expected of you.
Best of luck