I cant respond to that med, but I can tell you it is not unusual to recognize PPD some time after the birth.
I had PPD after my 2nd only. It freaked me out & I thought i should be able to "handle it" on my own. Well, recognizing that it is beyond your control & that meds might be the best thing - it is not a life sentence - it is a tool. I know many who have taken them for 6 months or a year or two & then they ween off & are able to manage from there.
If you have a good friend that you talk to /see most days, keep her informed & let her help "monitor" you. Keep a journal as well. It makes it easier to track your thoughts/feelings & behavior.
I was on Wellbutrin for 10 months & had my walking buddy keep an objective eye on me. It was like a safety net.
Hang in there, keep communicating w/ your Dr & your close friends for support!
P. : )