Hi OP.
My DS, now 18 months, was the most miserable and high needs baby I have ever come across. It was absolutely relentless for the first 16 months if I'm honest. It was day in day out of crying (the first 8 months) or whining/moaning (the next 8 months) and I was seriously struggling for a long time.
I tried everything; paediatricians, omeprazole, colic stuff, CMPA milks, tongue tie cuts, osteopaths, more sleep, less sleep, early weaning... he just seemed to hate every living moment regardless of what I tried. He was so miserable that I never wanted to leave him with anyone as they just wouldn't stand a chance. The only thing he really liked was being walked around in the sling outside, and so I walked and walked and walked and walked 😂 I felt so confused as to why this had happed and why everyone else's babies seemed calm and settled. It's really hard.
Nothing helped. I kept waiting for the 'thing', or the milestone, that would fix it and there hasn't been one. But I can say in the last month or so he has seemed much 'lighter' and less tormented. Nursery even say he is a lovely happy boy, which is something I never expected! He now loves playing manically and laughing with his older sister. It is definitely finally changing!
I don't mean this to dissuade you, or take your hope of a 'fix', but to reassure you to keep going, and not feel too disheartened if none of the milestones bring that change you are seeking. It can be crushing when you set your hopes on sitting/weaning/crawling/sitting, and it just doesn't happen how you hope.
Keep on going OP, it won't be like this forever
And if there's any karma, you will have a lovely easy toddler and not a threenager!