Is it normal that my brain can't memorize what i've learned?

It can you just have to learn to meditate like batman does. That's how I learned. Watch the Dark Knight series

I have the same problem. I had a hard time in school. Can you remember stuff better that interests you? When something interests me it's easier to learn!

Maybe you have ADHD or a form of it. Ive had it for years and only recently got diagnosed. Many people dont have the hyperactivity part as much as the short term memory/ distraction part. Just a thought.

Take Adderall or Ritalin.

(not the op)I cannot even remember things that interest me. I'll learn something that fascinates me, and I'll only remember about half of it. It so frustrates me, because I want to remember it, so I can think about it later. It's like the information falls out of my brain.

You are hardly dumb, and are a good writer.

Just watch a video, read a book or whatever with no intention of trying yo memorize it. If you find it hard to concentrate, dont force it. I sometimes be reading and feel like I haven't paid attention at all, so I go back to the previous page to read it again and then realise I do remember every word. I used to never write anything down in school but somehow the knowledge was just there in my brain when it came to exams.

Think of something you have a good knowledge of, like a hobby or something that you are interested in and think about how you gained thqt knowledge and maybe it will help you find the right way of learning for you.

Try to understand what you’re learning into details rather than just memorizing it it really really helps and also practice makes man perfect so continuous learning will soon make you a master in learning and you’ll soon grab content much faster and easier so be a bit patient maybe you haven’t gotten to that stage yet

If something is boring it is going to be harder, if not impossible, to learn.
When something bores us, our brains basically shut down.

I remember in school having to read social studies crap and would get to the end of a page or even paragraph and have NO clue what I just read.

Of course today when kids are unable to learn bullshit that is boring to tears, they say the kid has a learning or attention disorder.
No, that is not it. It is because some things just bore people.

It may be relevant to the method of you learning OP. You may not be a visual or auditory learner. You could be a hands on (kinesthetic) learner. A doer.