Constant brain fog?

Before college and during my freshman year, I never really had brain fog. My mind was always super clear, and I prided myself in my on-the-spot critical thinking, etc.

Now, 5 years later, I have constant brain fog and feel dumber. It takes me a long time to process simple things, my attention span has worsened, and I have a constant headache.

Have any of you faced this and gone about in a systematic way of solving it? I was thinking of limiting my screen time (hard, due to work), start reading more books again, fix my sleep schedule/diet, and exercise more, but these are really broad and my discipline has worsened as well. Idk how to get the ball rolling on this.