When I had my 2nd baby, I felt like you, only I didn't have any insight into how I was feeling, and just struggled on not able to get out of the big black hole I was in. Eventually we moved to a different town, and within two days I had a visit from the health visitor, and within about 10 minutes she asked "What has been done about your PND?" and I replied "What PND?" My baby was 18 months old by then, and she explained that if I'd been given help earlier, I wouldn't be still suffering. Back then, in the early 70s, medications weren't as good, and we'd never heard of talking therapies. I was given Valium, which made me feel horrendous, and like you, I stopped taking it. But my HV visited me every week, sat down with me for a cup of tea and a chat (Talking therapy!!) and within a very short time I recovered.
About five years after that, when a foster carer, I was asked to take on a child every other weekend, just overnight. Another foster carer would do the alternate weekend. The mother was having horrendous problems because he wouldn't sleep. When he came to us, I put him in his cot at bedtime, having started a routine of a bottle, a cuddle and a book, then singing a song, and putting him down. He would cry for about five minutes, then go to sleep. And sleep all night. Eventually the other foster mum and I met up, and he was having a very similar routine there, just by chance, and she was also leaving him to cry for a few minutes before he fell asleep and slept all night. Neither of us had quiet houses, I had four children, she had five. He still wasn't sleeping at home, and we came to the conclusion that it was her anxiety that was causing the problem, including the fact that when he did fall asleep, she would panic and think he'd stopped breathing, so she would go in and touch him to check. We were not anxious, so both of us were calm, and I think he picked up on that.
My system with babies who didn't sleep was a kiss and cuddle, put them in their cot, say night night and leave the room. If they were still crying after ten minutes, I'd go back in, (no light on) Lie them down, stroke their back or head for a minute, then leave them. I'd keep doing that, never speaking to them or picking them up, and definitely never taking them back in the living room, where the light, TV, company, would over stimulate them. It worked, but you have to be consistent. You can't do that for a couple of nights then decide to try something else.
I hope you get the help you need.