What could be the reason my skin looks dull these days?

Lately, when I look in the mirror, my face feels duller than before.
I'm worried because even when I use tone-up products, I don't look as radiant as I used to.
I'm not sure if it's because I haven't been able to sleep or if my skin is dry.
I thought it might be due to dead skin cells, so I tried exfoliating, but I didn't notice much of a difference.
I'm also wondering if I should be at the stage where I use whitening products.
I'm hesitating because I'm worried that adding more products might burden my skin.
I'm wondering if my skin tone suddenly looking dark is a temporary phenomenon.
How should we set the management direction in this situation?
Since this happened all of a sudden, I wondered if something was wrong with my health, but I don't think that's the case. I'm trying to take better care of my skin, but I'm not sure.