See a different doctor and have them examine you with a spotlight on ADHD symptoms. There's remarkably few doctors that are good at diagnosing ADHD, especially in certain presentations.

There's a lot of common misconceptions about ADHD and it's signs/symptoms, and those misconceptions are not exclusive to people without a PhD. So get a second or third opinion.

I'm on the gifted side, with an more inward presentation of ADHD, it wasn't until I was 39 that I even spoke to a medical professional about it. I was mediocre in school (often without trying, because I couldn't focus or sit long enough to do homework or study), and as I've gotten older and into my career in a highly technical field, job demands have made it much harder to mask my ADHD symptoms. I started treatment by medication and I've been able to sit and focus and do my job better and easier than before. I still have challenges, medication isn't a cure; medication has simply given me better control over where my focus lies, if I'm not working to direct my energy and focus into the right work, then I'm no better off.

Diagnosis is the first step, so if your doctor isn't up to speed enough to know the signs and symptoms, find one who is.

Until recently, adult ADHD was not considered to be a thing but evidence has shown that to be very wrong. A lot of people were told that people just grew out of being ADHD, and some do, but not everyone.

Your achievements do not and should not have any bearing on whether you are affected. You can have ADHD and be very well decorated in your achievements, even if you've never been properly diagnosed or treated for it.

The main factor here should be whether you think that you may have it, and whether or not having it may be holding you back. Make a choice whether that's something you believe, and go from there.