I am really sorry you are going through this OP
it can be a very tough and lonely place
places like MN that used to be quite supportive can be a bit funny now with people getting angry (wtf?!) if you do not follow their advice… and you will get conflicting advice!
You will have to feel your way through it and learn to trust your own instincts. it would also be good to get your H MUCH more involved as this is too k m’n UTC to deal with alone
one of my kids was very difficult as a two/three year old, he even bit other kids and he seemed to not always like me a as he hated being hugged or cuddled
he did not show emotions either which made him seem “cold”
things did get better though, he got help at school (social and emotional, also academic) at the tiny state school. He got corrected by his peers too, which is interesting, but it is a big thing they get from schools: be nice or nobody wants to play with you.
it was his sibling who once explained to me, that his brother does not show much emotion but that that does not mean he does not have them.
We tried to keep consistent and loving, and firm. Definitely needed two parents on board with that btw
he ended up doing well in school and being very sociable and having loads of friends
lastly: be very kind to yourself. Undiagnosed and untreated PND is very hard to live with (if you have that) and you need to be super nice to yourself and give yourself a break (emotionally and physically), you need a weekend to yourself with a friend maybe, let your H look after the kids. You need to recover
take care