You should not diagnose your child based on articles from the Internet. If your little one has any of the above symptoms, you should see your doctor for diagnosing.
If your child has been officially diagnosed with ADHD, I want to support you. Don't think it's your fault. Your task now is to accept the situation. I advise you to take ADHD as a feature rather than a problem. Each child needs an individual approach. And your kid needs it as well, regardless of diagnosis.
Often ADHD can disappear before the person gets to the conscious age (16-18 years old). However, this diagnosis can also stay with a person for the whole life, or appear in adolescence. In adulthood, it manifests itself somewhat differently: attention deficit prevails in contrast to childhood, when it is mostly hyperactivity.