How do you turn your brain on? Like activate study mode?

Cause it feels like mine is stuck in sleep/airplane mode. I try to read something to learn and the information goes through my brain like a sieve these days. I got to read it 3 or 4 times and maybe in a weeks time my brain is like, 'hey you know something.'
But most times it's snippets of information I remember from things I probably wasn't paying close attention to at the time...