I have 3 children and don't have diagnosed depression, however I did have pnd with each of mine - it hit me very differently with each one.
I do think that your best option is to talk to your GP/care team and see what options they suggest. If you've only been on the sertraline for a short term then I would wait until you are at least 6 months stable before coming off it (advise given to my husband by 3 different psychs), but I'm not a doctor. I do also know that at least 1 anti D is considered safe during pregnancy and breast feeding - but again, you really need to discuss this with your Dr.