I’m a bit late to this thread and can offer no advice not already offered - just wanted to add to the voices saying you’re truly not alone OP and it’s so difficult when you’re in the thick of it but to me you sound like a lovely person with her head screwed on right, well done for all you have endured and for soldiering on. If you were a ‘crap’ or ‘evil’ mum you wouldn’t be worrying about it as you so clearly are.
My twins were premature and emergency csection, they had a stint in NICU for being so tiny and it took months after getting them home for me to feel any sort of bond, like others have said I felt trapped by them, I went through the motions and that was all I could manage. DD was a screamer, it felt constant and when my mellow DS joined in I felt I’d break under the pressure. But, it does (and did for me) get better!
I have read as much of the thread as I can but wanted to offer the following in case it’s not been mentioned (probably has so sorry if I’m repeating):
Infacol or Gripe water for painful wind/colic - helped my DD loads as she was always struggling with gas.
Hungry baby formula might help too, DS was a tank and fed constantly too, I got him onto this at roughly 12 weeks and it made a lot of difference.
If you have a bouncy chair that helped with my DD after feeds and reduced her gas pains. Also with cot/Moses basket, try propping the head of the bed up (I used a couple of Argos catalogues) as this can also help with digestion.
My DS communicated with headbutts a lot and graduated to biting when he got his first teeth (gentle biting though) it’s not any sign of dislike, you’re his world.
Don’t be afraid to let him cry a bit, this isn’t popular advice here generally but if you know he’s been fed, changed and is comfortable and the crying makes it feel like the walls are closing in then step out of the room for a few minutes, take a breather - allow yourself some respite. You’re doing brilliantly OP and I wish I were close enough to come help - I hope your GP is helpful 