Oh, mama! HUGE !! It does get better. I have had PPD 3x now, after each birth. It does get better, I promise, though it sounds like it might take some tweaking for you to get there.
First thoughts I had are, are you breastfeeding? If so, make sure you are well-versed in the safety of the meds you're taking/interested in before going to the doctors. Make sure you have a prescribing doctor who knows you are breastfeeding and is comfortable working within those boundaries. I have taken Zoloft each time, varying doses with each birth. The first time, it made me drowsy. This last time (the 3rd), it gave me insomnia. You can change when you take your meds so that the peak of the meds hits when it matters most. I started taking my Zoloft (when it made me drowsy) at night so that I wouldn't get drowsy during the day. Maybe take your med early in the morning? Dr. Thomas Hale has great info regarding PPD and anti-d's.
Are you seeing a therapist at all? Depression is best treated when it's a combo of meds and talk therapy. Other things that have helped me have included taking a really well-balanced omega oil blend (I like Twin Labs Complete EFA), using the sun as a therapy (spending time outdoors in the direct sunlight or using a light therapy lamp), scheduling time for me to go out alone, like grabbing coffee or meeting friends, and taking up a hobby. I know it sounds simple, but they can really help you out.
I truly hope you find the answers you need to find. I hope you have a good provider who can support you in your medical decisions. And most of all, hugs. I've been there.
Wife to , mama to , , , and - bonus mommy to !