This sounds rough OP, hoping you can get some advise to help. 💐Sleep really does help with PND in my own experience, which is easier said than achieved.
Would you be open to giving a bottle at night, to see if that would stretch the first sleep? This didn't work on my first, as they refused bottles, but has worked a treat on my second. I use ready made formula bottles, to minimize the nighttime prep. They're expensive, but I get two nights out of one bottle. I give it around 10pm, and usually get a 4-5 hour stretch after. I would prefer to EBF, but pumping is a lot of work and I needed to prioritize my mental health this time.
Other things that worked (a little) with my first DC (who was a frequent waker):
- outside first thing in the morning to set they're circadian rhythm with sunlight
- outside as much as possible tbh
- feeding them as much as possible during the day, to get the calories in before night time. Don't think this worked too much for mine, as they just got extra roly poly 😅
- waking them up at a consistent time in the morning, to book-end the day
- consistent bedtime routine & time
- sleep sack & sound machine
- sticking to wake windows pretty religiously, and aiming for one sleep in the crib a day if possible. Even if it was 10 minutes I took it as a win.
- trying to make the biggest nap the one in the middle of the day. Took a lot of contact napping / feeding to make it happen
- co-sleeping using the safe sleep 7 guidelines
- this didn't work for us as mine hated being spoon fed, but baby cereal before bed is meant to be great for sleep too
- FYI it took 1-3 weeks after implementing any change to see a difference, so consistency is definitely key.
Just to add, 6 months is a particularly tough age I found. They're so alert, and processing everything, which massively impacts nighttime sleep. Plus, they're getting used to solids, and teething too. Every breast fed baby I know feeds to sleep, so you're definitely not doing anything wrong. It's a natural way to soothe them, and often the fastest way.
At this age, my first was up every hour. They're now fast asleep in their own room for the night. This was a very gradual achievement, but I promise this sleep deprivation won't last forever. ❤️
Frequent night wakes are so hard with PND, as it's hard to stay positive in the middle of the night when you know there's more wakes ahead of you. I found journalling on the notes app on my phone helped a little, instead of doom scrolling. Or downloading a trashy romance on my kindle app - anything to make it easier to stay awake and not catastrophise. Plus therapy obviously.
Hope things get better for you!