“When I was a kid, I had the sense things were more difficult for me,” Tiffany Bui recalled. It was hard for her to focus in school, and she was often forgetful. Throughout her life, she said, members of her family criticized these traits as faults...Ms. Bui’s story is not uncommon: Many women and people of color are only now learning, after years or even decades of difficulty, that they may meet the diagnostic criteria for A.D.H.D., thanks in part to a wave of creators on social media trying to spread awareness.