Ah I feel your pain.
We tried all sorts of madness/nonsense with our PFB as we were so desperate for sleep.
None of it fucking worked.
With our second, she was EVEN worse if possible?! Oh she was.
We had silent reflux, tongue and dairy intolerance to deal with. But what helped was just accepting that all the books about routines were just a tool to make me feel inadequate.
Stop researching, you’ll drive yourself mad working out possibilities.
Go inside. If he wakes, he wakes. A new day tomorrow.
With my second, she got better at naps and settling because I had to leave her every now and then to deal with toddler. I also had to feed and cuddle her to sleep more than I would have liked because of said toddler (easier to stick a baby on the boob at bedtime).
So basically I’d feed her to sleep then put her down and do my thing for a bit. It was kind of like sleep training but not really as I’d be straight back ASAP.
But in short - life had to go on. So try that for a bit. Yes have a loose routine - wake at the same time every day and aim for bedtime at the same time as if you had an older child. But as babies change so quickly (as I found more believable once I’d had another baby), there’s no point getting too hung up on things.
This Too Shall Pass