I'm putting a caveat right up front here - it's never a great idea to self-diagnose. That said, I do get a lot of questions about what is ADHD and what might be something else.
One of my consultants recently introduced me to a wonderful resource for a top-level way to sort this out. Misdiagnosis Mondays, put together by Dr. Megan Anna Neff, is a series of Venn diagrams for ADHD and Autism symptoms and behaviors as they relate to other disorders. While charts don't replace talking with your medical specialist, they can at least help you think through the questions you might have.