4.5 mo baby, going insane

Our daughter is 4 and a half months old. She has always been a horrible sleeper, from day 1, even in the hospital, nurses hadn't seen such a difficult sleeper in a long time.

My partner has severe post-partum depression and OCD, so I have to do all sleep related care for the baby myself. The last time I've slept more than 6 hours in a night and more than 2.5h-3h uninterrupted was the night before our little girl was born. My partner sleeps in a different room because lack of sleep makes her symptoms significantly worse.

During the nigh, she up to very recently woke up trice. We put ber to bed around 19:30 to 20:00. She then sleeps to 22:00, when she wakes up and drinks a bottle. The she sleeps again untill 01:00, wakes up and wants a bottle, and again at 03:30. She would wake up around 5:30 to 06:00 and refuse to sleep any further. Again, up to recently, this really was just a 15-20 minute wake period for her and me, then back to sleep. I would put everything for the bottles in bed with me so I can make them without getting out of bed.

Now, just a few days ago, she had a night where she woke up every hour. Just for a few minutes until I could put her back to sleep. Since then she has been an even worse sleeper. For the last 4 nights the schedule has been: go to bed at 19:30, sleep untile 23:00, and then once she wakes up at 23:00, she refuses to sleep anywhere but my arms. As soon as I put her back, she will start twisting and turning and let out little cries. Im under the impression she isn't even awake at these points. Im now into my 4th night where I'm barely sleeping (less than 4-5 hours a night). I feel I'm going mad because of how tired I am. I can't function at work because I'm so tired, and I'm terrified of driving to work because I'm worried I'll fall asleep behind the wheel so I've worked from home since this started.

I am going mad looking at sleep training schedules. Our little one just doesn't like naps. The daycare aay they have never seen a baby that napped so little and clearly wasn't tired. She at most naps 2ce a day, one 30 min nap around 10 and one 45 minute nap around 16h. Again, she doesn't seem tired at all. She is happy, looks around a lot, smiles, and is excited.

I've even bought a course (which I regret but was pressured into by my MIL, since all the information in it is the same as I can just find here online) and it just doesn't work. All of it seems to assume your baby naps a lot and has bad nap schedules and so on. But our baby just doesn't seem to need sleep. There is no nap timing to be scheduled because she won't nap.

And for sleep at night, she does fall asleep on her own. It's just that after a while she starts waking herself up.

Please help!