Is there a way to really know if i have adhd?

No gold standard: Adhd is a clinical diagnosis. You need someone with experience and expertise to make the diagnosis, especially in adults, since it often is a matter of excluding other causes for the same symptoms. Get assessed by a reputable psychologist or psychiatrist experienced with adhd. You can't "catch" adhd as an adult, so a key issue is whether you had symptoms during childhood. If not, it's not adhd.

Neuropsychology test: The most definitive way is to have a neuropsychological assessment. The results can lead to the appropriate treatment, whatever the cause.