I'm joining the Coast Guard but at MEPS I was denied military entry for ADHD, what can I do?

At MEPS I was completely honest and told them that I was diagnosed with ADHD in 3rd grade (what 3rd grader doesn't have ADHD?) I'm almost positive I don't have it. I sent in my medical records only to find out that MEPS denied my entry. How can I prove myself? I want to join the Coast Guard and I'm not going to give up. I believe my recruiter said something about a review board? Who knows anything about this? FYI I was FBLA (Future Business Leaders of America) president for 2 years and I competed at the state level in parliamentary procedures. I was a member on my schools Knowledge Bowl team, I was one of the top students in my schools leadership cl, I was my high schools ASB Business Manager. I helped/plan nearly every event my school had. I am such a hard worker how can I prove myself!? Any help is greatly appreciated!