If those three fundamentals don't improve anything, you should then consult a professional to help. If the professionals can't help then you can try out personal suggestions from others (like this thread). This is just the path in order of most-likely to least-likely solutions.
It is possible that you have an inherently bad memory. It seems like long-term memory from your post, but some more clarification would be good.
No sweat. Look into Anki flashcards and do all your note taking for things you want to memorize long term. For all other forms of notes, just have them easily accessible via search or time/date stamps. Gotta craft systems using reliable tools as crutches to improve on any innate abilities. I may not be able to dunk on a ten-feet basketball hoop, but I sure can with a trampoline!
Cheers, and I hope you find a reliable solution soon. You deserve it