How are you doing today Amy?
I think your DH needs to MTFU and take the baby out for an hour or so every day. for one thing, he needs to get to know her better, let alone giving you a break. And when he's with her, he needs to not be texting you! My DH took DS to the park for 2 hours when he was about 7 weeks old. He had a bottle of ebm, which he used in the first 20 mins, and DS screamed the rest of the time. He sent me a text telling me they were having a lovely time, because he knew I needed 2 hours to myself ( I had a bath, read my book and did my toenails, bliss!), and he also knew he needed to work out how to calm ds down.
At 4 months, she is old enough to go for a while without a feed, even if she's crying, some distraction like a walk in the park may send her to sleep or calm her down.
If you get a little break, it will help you feel like yourself again so much, I promise. I know it's not the answer to pnd, for that you need to get a new dr and some different meds, but it will help!
As for the feeding, I honestly don't see how the odd bottle of formula will do any harm, especially if it means you can go to the gym, or out for a bit on your own.
Or, I run in the evening when DH gets home, I only go out for half an hour, and just after DS has fed, so I know I have at least 45 mins to run and shower before he might need another feed (evening cluster feeds!) would that be an option?