Trouble with Memory - What could this be?

For the past 6 or so years, I have had trouble with memory in a certain area.
When someone is spelling out a word to me that I'm not familiar with, I cannot visualize the spelling in my head. I have to ask them to spell it out very slowly, otherwise I cannot comprehend it. The same goes for a series of numbers (for example: a phone number). I know this isn't normal because I don't know anyone else who needs something to be spelled out as slowly as I need it to be.

I have other related things if it will help identify what this could be.
When I want to write or type the following sentence, for example "the boy caught a fish." I will very frequently replace "a" with "i". The same goes vice versa. "However, I am timid." I will frequently put a "a" instead of "i".

What could this be? ADHD? Dyslexia? I haven't had any luck with my online research. Any ideas?

By the way I am a 21 year old male.
Thank you

Are you schizophrenic or schizoaffective? It could be mild cognitive impairment from one of these disorders. I have it, and it has affected my memory so badly that I had to quit driving and move into an assisted living facility. I am 57 years old though. But, these illnesses attack the brain at young ages.

-- Sun Feb 26, 2017 1:07 pm --

Dyslexia is possible too though.

I had a mild stroke due to drugs in my twenties and from that moment onwards my memory was affected. I have since researched various nootropics and have found many that have improved my life.
To start I would suggest some acetyl l carnitine/dmae pills/CDP choline/Alpha gpc, these all boost your acetylcholine levels in your brain, the chemical responsible for mental illness and is often lacking in alzheimers patients. An add on would be Co enzyme 10 which offers crispness in my thought. Eating two/three eggs each morning will make a big difference as well as they are rich in choline. I nearly forgot... I also take gingko biloba capsule with my coffee each morning to improve blood circulation in my brain. I have tried not taking it and for my condition can say it is a must. Lions mane mushroom has been proven to increase nerve cells within the brain. The doctor who discovered it won a Nobel prize, so keep it in mind. A good Omega 3 supplement is also essential to maintain whatever brain matter you have.
A teaspoon of Moringa powder will also switch your brain on.
Depending on where you reside, you can start looking at stronger nootropics such as Piracetam, Aniracetam and Phenylpiracetam. These are stronger and may require a prescription in certain countries. D read up on them...
I have not experienced any negative effects with theses substances. All the best to you !

I have finally realized that my poor diet has greatly contributed to my memory problems and has exasperated my mental health issues. You may want to seriously consider your diet...If you have not already done so.
Eat lean proteins and plenty of veggies such as broccoli and cauliflower. The webs has plenty of resources for tasty recipes if you are not a fan of veggies. Or you can just choke them down because you know you have to.
Avoid sugar and complex carbohydrates. Learn how to properly cook brown rice. Definitely avoid preservatives. (I also avoid GMO products)
It goes without saying we should all avoid drugs not prescribed by a doctor.

Sometimes I tend to block things out. Rather than comprehending, it seems i have programmed myself not retain information. I have had my share of trauma shock events so it may be a defense system I built up rather than dealing with the situation.