Hi, sonnynotsunny! ADHD is a real neurobehavioral disorder, and usually people who claim it isn't do so because they fear the implications. For example, they may have a loved one with the disorder, and prefer to think that it isn't real and that there are no issues at hand.
To me, the diagnosis answered a lot of things that have gone wrong with my life. It answers why I am knowledgeable and intelligent, yet disorganized and oblivious to things right in front of me. I used to call myself stupid, but learning about ADHD was a relief. It increased my self-esteem and enabled me to have better insight.
If you are concerned, I would suggest visiting a psychiatrist so you can get a more rigorous diagnostic.
Best regards