Does Difficulty In Concentration Suggest ADHD?

I have extreme difficulty concentrating, to the point where I space out unintentionally almost constantly. People mistake it for laziness, but no matter how hard I try, I can t fully bring myself to concentrate most of the time. But, if I m interested in something, I can stay focused on it for a long amount of time. This is why people think I m just being lazy. I also tend to forget things a lot; I ll ask someone the same questions multiple times within a few hours because I forget if I asked them or if I just imagined asking them. This has been going on for most of my life, but no one ever believes me because I wouldn t get good grades if I was like this and I wouldn t be able to focus enough to draw. Some people have suggested ADHD and DID (because I also have changes in personality, but they mostly have to do with a constantly changing and distorting body image), but all I really have to check are online symptom checkers and articles on said disorders.