Seriously... how do I get my brain back.

My employer normally only gives 10 weeks for child birth, but with the help of my therapist, I was able to find a psychologist to sign off on me being unable to return at that time due to mental health reasons. This landed me a whopping 6 months, which just ended last week.(I had to bust ass and pull teeth to get that)

So now I'm back at work. I work in finance and handle extremely sensitive matters for our wealthiest clients. My job cannot afford stupid mistakes.

So here I am now.. back at work.. staring at my screen.. I cannot wrap my head around what I need to be working on. I am stupid now. I cannot multitask.. I can't critically think. A certainly cannot solve complicated sensitive financial problems. what do I do

I need my brain back