As someone with inattentive ADD, I must say that what you describe doesn't sound like ADD at all to me.
Everyone gets bored and lets their mind wander when they have to read boring books and listen to boring talks. Everyone misplaces things when their attention is elsewhere. Imaginative people daydream. We all have mood swings. It's part of being human.
I definitely wouldn't take a psychoactive drug based on such a quicky diagnosis. Proper diagnosis requires a battery of tests and evaluations.
It sounds like you would be better off looking for a different shrink.
You sound like an intelligent person -- you are getting good grades in school, and you are questioning the logic of what a person in authority has told you. You will do fine in life!