I know a lot of people do very well on sertraline but I do think it makes you feel worse before it makes you feel better.
When I had PND years ago I switched from Amitriptyline to Sertraline which I regreted. The sertraline made me feel wired and tense, and killed my libido. I was on it for about a year, I think. In the end I decided I'd rather take my chances and see how I felt taking no ADs because I just didn't feel like me on Sertraline, I felt like a pissed off robot.
So my GP switched me to Prozac temporarily as that's meant to be much easier to withdraw off. I was in it for about 6 weeks, didn't like it either so just stopped and sent cold turkey (I know this isn't recommended though).
Then 2 years ago, when I started getting peri anxiety and low mood again, I tried Sertraline. After the very first tablet I didn't sleep a wink that night. After a few days I felt I was getting worse. My anxiety increased a lot. I had daily diarrhoea and zero appetite. I persevered with it for nearly a month, but then had a couple of really nasty episodes where I felt I was going to pass out as I felt so tense and panicky, so I stopped.
I don't know if things would have improved if I'd stuck with it for just a couple more weeks, but I truly couldn't stand it anymore.