It is so scary when you feel like you are losing your focus, and I panicked thinking something was wrong with me. But please don't worry, 'baby brain' is completely real and usually peaks around the second trimester when sleep gets disturbed.
It's basically caused by high progesterone and sleep deprivation, often starting around week 10 to 12. There's no medical cure for it, just laugh it off and keep a shared calendar with your husband.
When I was staying at my parents' house, I would put the milk in the cupboard instead of the fridge! My mother used to laugh and say this 'bhulakkad' nature is just because all my energy is going into growing the baby.
According to my app, brain fog can actually start as early as the first trimester due to the massive surge in progesterone. I started setting phone reminders for literally everything because I became so forgetful!
Look, it starts whenever your hormones start going crazy, usually by the end of the first trimester. Just start writing things down on a notepad instead of trying to remember everything, it's totally normal.
I was forgetting my keys and appointments constantly in my second trimester. I even asked my hospital's nurse coordinator if it was normal, and she laughed and assured me it happens to almost every mom-to-be due to hormonal shifts.