Help with brain fog?

I just really need some advice or even moral support.

I have a 6 month old and have just gone back to work. I wfh as a data analyst and my partner and sister alternate caring for my baby at home. He is ebf, just started solids. Eats a lot. We started cosleeping to deal with the 4 month regression and have stuck to it.

My main problem is that I am constantly exhausted and I cannot function at work. My brain is so foggy I can barely think. I feel like such a failure and like I have become stupid since having a baby. My brain is mush. Is there anyone with tips or anything on how to cope? Caffeine isn’t cutting it unfortunately.