OMG OP, I recognise and identify with you a whole lot.
This was me, pretty much, about four years ago and no, it is not trivial - it is horrendous. The things he says, the level of pure 'nastiness', the monitoring, the undermining, the endless blaming.... I could go on. It is a campaign being waged against you. A war. Somewhere along the line - and you say this has been your life since you were pregnant - he decided (without telling you) that you are his enemy. I am so, so sorry this is happening to you. It is abuse. And there really is nothing you can do to change thing. He is not interested in making you happy in the marriage. His only interest is control. And you cannot - for your sanity and health of your child, allow this to continue.
We also had years of infertility and IVF. It is such a struggle. The trouble is, looking back, I think the infertility and all the grief around that masked the build up to abuse. I was miserable and getting more desperate, he showed signs of bullying when I became emotional. His temper and anger were scary before, but the incidents were relatively rare. When I got pregnant, instead of being proud and admiring of me (I was bloody proud and wanted to be admired for the fact that my body was finally doing what I wanted it to) - he withdrew affection from me. That was awful enough, but after the baby was born he was exactly like your DH is now... dreadful. He undermined me, picked holes in every decision that I made - every, tiny decisions about nappies, feeding, naps etc. All was questioned in a haranguing way, interrogation-style. And I was a SAHM! So when he came home from work there were endless distressing post mortems. He was overprotective of the dc, but I think that was really a mechanism for 'proving' that I didn't care enough and that I wasn't good enough. Everything was an implicit criticsm of me, and then there was the out-and-out criticism. He saw everything as a power battle. There's nothing you can do to defend yourself as nothing you say or do is going to convince him. He doesn't want you to feel ok.
Your brilliant mother is on your side. She knows. Please tell people in RL. And get legal advice. Start getting your ducks in a row and you will feel stronger.
You will get stuck asking 'Why?' over and over again (if you're anything like me). If you can, try and avoid that. There is no answer. If this is an itch you can't help but scratch, the Lundy Bancroft book is good. But the upshot is that your H is very unlikely to change. You haven't done anything, this is the person he is.
There might be lots of reasons... but they're all to do with him, whether it's boarding school (tick), hates his mother (tick)... whatever it is, this is him. It is a shock and may take time for you to come to terms with the fact. All your dreams take a severe knock. But gather support around you. Tell your family and supportive friends, and you'll get through it.
Don't feel ashamed that your child is so young. Be proud of the fact that you are protecting dc from growing up in a hostile environment where his mother is being abused.
I am now divorced. It took a long time as he became even more enraged that I dared to divorce him, so he was obstructive and hostile and intransigent. I just had to dig in and keep going. When you get a solicitor, get a really tough one, who has had experience of aggrieved, vexacious and abusive husbands. Best to err on the side of caution there.
p.s. what you say about weekends chimes with me. They were awful. Any expectation I ever had about nice family time, a bit of a rest etc were always dashed and by Monday morning I would be a mess. It is hard to explain how it makes you feel, but people will definitely believe you. It is also surprisingly common for abuse to start in pregnancy or just after the birth.