If you think you have ADHD, I recommend starting with an online assessment.
After that, you can see a qualified, licensed healthcare professional for diagnosis and treatment.
An assessment can be done by a psychiatrist, psychologist, neurologist or a family doctor who is trained in ADHD. A thorough assessment requires a complete physical and psychiatric medical history and some type of screening to rule out any possible physical disorders, so receiving an assessment by a physician at some point is recommended.
In my opinion, an official diagnosis isn’t necessary unless you choose medication as a treatment. An official diagnosis can also give you peace of mind. You might want to get the diagnosis and discuss medication with your doctor. Ultimately, it’s up to you.