Hope you're well:-)
I think you have provided enough evidence to answer your own question. However, what I'm interested in, is why you haven't already taken this option and been tested for A.D.D? You've suggested symptoms that fit in to the diagnosis, but your only real evidence for not having it is that you don't have behavioural problems & can concentrate on things you like. A.D.D doesn't necessarily mean having behavioural problems; it can sometimes mean a hightened frustration when things go wrong & misplaced emotions, but not necessarily behavioural problems.
The key element to conditions such as ADD & ADHD (symptom-wise, they're closely related) is that the person with it has a displacement of energy & attention, which can impact on learning behaviours. There can also be 'spectrums' of behavioural symptoms- someone can be more ADD than another person, but IMO I think this influenced by background & environment.
Geographically, ADD/ADHD is more likely to occur in white, low-income families, but that's simply down to statistics of reported cases. Additionally, ADD/ADHD is what is termed ' a Westerners condition'- it occurs in the developed world, but cases of it in more underdeveloped countries are rare. It's more likely to occur in boys and diagnosis age is usually in childhood to late teens.
I wouldn't necessarily take, such things as your geographical information in to account though; if you think you need a diagnosis- go for it.
I've just read over your original post & you said spoke to the school psychologist, but didn't say what they had diagnosed you with?
Also- if you do have A.D.D, how do you think a diagnosis will change your life? I ask this, because not all ADD & ADHD sufferers have medication and for some, CBT strategies, diet changes, focus & memory exercises & planning strategies can help with day-to-day issues of the disorder.
If you don't have any significant learning difficulties that have been picked up in school; you may simply need to start trying to self- manage & start controlling your learning behaviours. You've recognised that you are having problems, so that's a start! Well done. You may not have an attention disorder- instead you might simply be a normal teenager who is having a hard time with the motivation & focus. Are there any workshops at your school or in your area that can help with your grades- for example, homework or study groups?
We can all feel uninspired & unmotivated by things we have to do, instead of want to do- but that's life! Kick in a time plan for your homework- stop procrastinating & trying to blame attention disorders and focus on your academics.
Good luck in your exams!