The only way to know for sure if you have ADHD or not is to get a thorough professional evaluation. There are several conditions that overlap with ADHD and sometimes look like ADHD.
You can start with a self-test:
That can help you know if you might be on the right track. Then, seek an evaluation:
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism