How often do you go on outings? When did the symptoms generally start? Was it around a time you started taking caffeine or taking more of it than before? Are you on other psychoactive medications that could affect your brain?
Regardless, if you're taking such a large dose of caffeine even occasionally, it could drastically affect your adenosine receptors, and that's only going to cause tiredness, speech slurring, brain fog, etc to continue EVERY day until you've been without caffeine long enough for them to return to a baseline.
Personally, I'd suggest slowly decreasing your caffeine intake. Most people say "just quit taking it" but that can lead to some really annoying crash and withdrawal symptoms, so I'd say slowly reduce by maybe ~50mg per dose, each week or so, until you're around 100-200mg max on any given day. If it doesn't work out, you can always go back to your current caffeine intake, but if it does work out, you've just saved yourself a big headache and potential medical problems.
I can promise you, this is not a normal bodily reaction to have at your age, and you're already hitting the recommended safe human limit if you ever take 400mg. To be clear, I'm not here to judge you. Just like most other people here, I think we're all just quite concerned for your health and safety.
"geriatric" was an old, now antiquated term for just "if you're past this age, you're at a higher risk of complications with pregnancy". It's not used anymore. (as the article you linked states)
"geriatric" is a loose term with no defined age range, but I can assure you 99.99% of people would not call you even remotely close to geriatric because you're in your 30's.
Then that should probably indicate to you that something else is the problem. For example, those tests don't indicate if you're getting enough physical activity, if you're eating too many 'processed' ingredients known to cause complications in high quantities without directly affecting vitamin levels, if you have a sleep disorder, if you're having too much caffeine, if you're breathing in air pollutants, if you have any number of genetic disorders, if you have certain damage to your organs, etc.
Talk to a psychiatrist. If they think it would be good for your situation, then it is probably good. Until you do that, you have no clue if it will help you or hurt you. It could improve your situation, or it could make you forget to eat, make your sleeping worse, give you worse brain fog, withdrawal symptoms, extreme anxiety, or even a heart attack.
Stimulants are controlled substances for a reason. Please, talk to a health professional qualified to issue prescriptions for stimulants, specifically about the possibility of stimulants for your particular issues. (i.e. don't just ask for tests, suggest the option. Doctors are willing to consider options when presented with them by the patient saying they want it, especially since a big barrier to people improving their health is often unwillingness to participate in a given habit or schedule of meds)
Oh, and consider a sleep study. That can catch many things that won't show up on things like blood tests, and is very, very, VERY relevant to your specific symptoms.
Many conditions are never identifiable through blood, nutrient, or physical analysis of your body via scans and tests, and are only identified through symptoms, trial and error with different medications and known coping techniques, identifying changes after altering behaviors, etc.
The symptoms you are having are not normal or to be expected, they are clearly very impactful to your life, and the fact more basic tests like blood/vitamin tests haven't identified an obvious cause signals you could possibly have a major underlying condition that could potentially be extremely serious.
Please, talk to a psychiatrist if you want to see if alternative stimulants could help, and get a sleep study done to understand how your body handles it and provide actual insight to your doctors.