I'm not sure how to explain it, but when I sit down to read a peice of text, my eyes see texr, my brain parses text, but that's about it. Its like my brain is "out of foucs".Often times I have to run over a single sentence several times before I'm able to extract any meaning of it. On to0 of that I cant seem to fully read anything whether it be an article on the internet (which usually gets roughly skimmed and closed) or a book (which I'll skip through beefily and close)
When I was a kid / teenager, on the other hand, I could read anything fictions or non-fiction, technical or scientific cover to cover if I wanted, and even maybe get somethingout of it.
Read a lot (and writing!) even if "nothing sticks". It sure will feel frustrating, but don't worry, it will improve again over time "simply" with practice. Don't feel abnormal, all this is quite ordinary as you grow up and more and more "stuff to think about" accumulates. It takes practice to get to a brain-relaxed state again. Mindfulness, meditation etc of course can help a lot too.