I was officially finally correctly diagnosed at the age of 38. From my early 20s until about that time, I was experiencing very much the same as you’ve described.
If you genuinely have ADHD, you need to know that this is a condition that can quite possibly destroy, over time, your career if it’s not managed correctly. The seriousness of this can not be overstated, which, as you have described, I think you are starting to understand for yourself.
It’s critical that you get a proper diagnosis from a well-informed clinician without delay. The effects of ADHD compound over time, it snowballs, i.e., lost jobs, bad reputation, missed promotions, damaged relationships, earn less money, not to mention a massive hit to your self-esteem.
The quicker you get to the bottom of this and get your work challenges under control (with or without medication), the better off you’ll be.