Sending all the hugs in this difficult time.
Firstly - It sounds like you're juggling a lot, especially with everything you’ve faced during pregnancy and after giving birth. Feeling like you're stuck in that heavy, clouded space between "I'm supposed to feel better now" and "I’m not okay" can be so draining, especially when you’re trying to mask those feelings 24/7.
You’re not overreacting — your feelings are real, and you have been, and are going, through a lot. Your support system loves you and wants the best for you.
Now,
Post partum depression and anxiety is actually said to peak around 2-3 months. So keep holding out hope that it'll get better.
I would suggest talking to a doctor immediately and also finding someone to be completely open with about this struggle, like your mum and/or your DH.
My DH was really looking forward to being a dad, and it took him a couple of months to finally admit that he felt like he was drowning in the difficulty. We're only 4 months pp, so we are still working on that together. He said just being able to talk to me help, and now I ask him every day how he is going and each week we vent our frustrations and then talk about what has worked and if something needs improving.
I'm not from the UK so not too sure what they have there, but we have a PANDAS hotline for confidential chats about depression and anxiety. There's also free parenting help groups where a parent/s can spend a few days at one of there facilities to work out parenting or baby issues.
And don't think of this baby as a death sentence, a solution can always be found. If you work out a system with your doctor, DH, mum and employer, then give that a few months to see if it works. If worse comes to worse, there are things like temporary (or long term) foster care.
These help lines, respite organisations, etc all exist for a reason - you are not alone and not the first to feel this way.