My wife was undiagnosed until she was 26. When she started on medication there was no immediate difference that she noticed. She had always been very good academically and did well in high school, uni and work so she was torn about whether she really even needed the meds given how well she got by. It became pretty clear over time as she started though that it really helped with preventing her becoming overwhelmed and helped her stay on task much better. Now she wonders just how well she could have done in high school and uni had she been diagnosed earlier.
All that said, ADHD is different for everyone so your mileage may vary. Give it a little time and follow the doctor’s orders and see what works for you. We went through a few different medications before finding one that really hit the spot!
To be fair, this one is common on Facebook because it’s the stupid top auto reply thing that is way too easy to fat finger when browsing listings