I've Had ADHD For Years, However Doctors Would Not Prescribe

I've had ADHD for years, however doctors would not prescribe me mediation because they said there was no history of my ADHD - although there was history of behaviour issues in school, low grades hyperactivity. For years I've been forced to purchase ADAH mediation on the side. I'm tired of doing this - but without medication I simply cannot focus at work. I went from a C student in high school to straight A"s at Northwestern University. I dont know how to go about getting a prescription and doing this the correct way. I was hoping there may be on online doctor that I could work with to get this started.