Hi N.. Congrats on your new son! I know how your feeling. I didn't have it for long and didn't require medication but I remember saying to myself at the 6 week mark, if this doesn't get better in a week I need to go see my doctor. Funny enough the following week it just lifted like a rain cloud had gone away. It's a helpless feeling. I don't think I ever felt so alone in my life. I didn't want to talk to anyone, see anyone and I remember looking at my son and thinking I had made a huge mistake and how was I ever going to cope with this. People telling you it will get better doesn't help a bit, at least it didn't me but unfortunately it's the truth. Your doing all the right things, you've seen your doctor about it, your on meds and your here asking for support.
I am happy to report that now after 5 months I feel so much better and am really truly enjoying my son and love him and my daughter more then life itself.
If your spouse/partner can take over a few night feedings and let you get some rest and you take your meds and keep yourself hydrated and fuel your body with good nutrition, I promise you'll be feeling better very soon.
Somtimes a mantra will help at the really bad times. My personal one at that time was "this too shall pass" but whatever comforts you can help. In moments when it's really bad just repeat it over and over again until your mind clears and your better able to focus.
You hang in there and continue to reach out when you need to. I found it helpful to take a few hours away whenever you can to get out and do something mindless like a pedicure or even a stroll around the mall to window shop, a drive through town, a grocery store run when it doesn't matter if you come home with nothing. Just something to occupy your thoughts that are mundane and don't require a lot of energy and effort.
Good luck and I hope your feeling better very very soon.