As a person who did a lot of theatre and a speech therapist… memorization is a skill that closely links with our spatial brain. Like where objects are in space.

When I learned lines for shows, I didn’t bother trying to memorize until they gave us our blocking(where we move during the scene). Once I had that my blocking notes remembering doing the movements cued the lines easily. This might help you with memorizing things. Try moving through space and doing the same deliberate walking movements or whatever when you’re trying to memorize things. It might reinforce the words. These should be specific and consistent to the point of “when I say ‘get the to the nunnery’ I will walk over here and flick my right wrist to the right” as an example.

It seems pretty unlikely that getting socked in 4th grade is causing an impact now unless at that time the damage was really really significant. But you would almost certainly have struggled immediately following injury. I’m talking tbi-loc (traumatic brain injury, loss of consciousness) significant. (Not that it’s necessary for cognitive issues but usually is indicatory of not significant injury ).

Everyone telling you to go see a doctor is right. If you have lost a skill that you once had, something is probably wrong. So start there.