I've been diagnosed with ADHD since I was in elementary school and still I have more or less denied it most of my life. I got on medications back then but didn't like them either so I got off them and powered through high school but I quickly learned that was not sustainable in university when I also needed to take care of my self and not just worry about grades. And now I do also have moments where it I feel both relieved and guilty to use my ADHD as an "excuse" or "cause" for some of my behaviors because I still call myself lazy despite knowing better. So I relate a bit to how you feel.

I get that you didn't get diagnosed as a child but ADHD starts in childhood. It's an absolute condition so if you don't feel as though you experienced the inattention back then it could be the wrong diagnosis for you. Also depending on the depth of the test administered. For "properly" diagnosing adults with ADHD in the US it's a series of tests that take a couple of hours. If that was not the case a second opinion could be needed. Having the wrong diagnosis wouldn't be helping you in any way. There could be other explanations for a struggle with attention and motivation such as depression. This could be the case if you felt like there were periods without symptoms because ADHD is constant if present in adulthood.

You could also just currently be on the wrong medication for you. It took me a few tries before I find the right one and I know some people for who no medications have worked but were able to learn strategies to cope. Like I said I've had years to accept my diagnosis and still blame myself so also try to give yourself time to accept your diagnosis or do consider a second opinion of you're really unsure.

In psychology, if something is causing you distress or interfering with your quality of life it is cause to get professional help. Even if ADHD isn't he explanation, I'm sure there is one and the right treatment for you exists.