I'm so sorry.
Give yourself time. It might not be what you want to hear but it took me months before I stopped feeling that fuzzy headed feeling and not being able to do anything.
I felt the same about ttc after dd2. We held off for a while so I could recover a bit mentally and physically. Our subsequent pregnancy, while fairly short, was stressful.
I ended up being signed off sick for about 6 weeks after dd2 and then doing a phased return. My doc and boss were fully supportive of this (in practical terms in meant my boss could access money to cover me) is that a possibility for you?
I found taking things right back to basics helped a bit. Do the minimum to get through. Greif is overwhelming and exhausting, your brain process a lot in the background which is why everything feels such a struggle. Allow yourself time. Feed, clothe and get the kids where they need to be, kisses and cuddles when they need them and forget everything else. My house was a tip for weeks after, I couldn't cook a meal or even decide what I needed for the shopping. Ask for, and accept as much practical help as you can. It is much, much harder than you might think (and others might think) but you can get through it. Life is very different but you find a new normal.
Sands are brilliant. I found I was very lonely afterwards, like my world had fallen apart and no one understood, then I went to a sands meeting and met people who did understand. It has helped me hugely.
Whatever you do don't beat yourself up, be kind to yourself and do whatever you need to to get through. Greif isn't just tears and heartache, it's confusion, fuzziness, anxiety, anger and a whole world of other emotions. 💐