Most Severe ADHD EVER?

Ok so anyway I'm in 11th grade and I've noticed something unique about myself… I have incredibly poor concentration. I can't concentrate on a task for more than a few minutes. It doesn't matter what task it is, I just can't focus on it. I have failed 3 grades because of this. If the task is boring like math or English, or if the task is fun like Minecraft or YouTube, I can't focus on it. I don't think I've ever played video games for more than 5 minutes without getting distracted. I would love to build all kinds of cool structures out of legos, but I've never spent more than 5 minutes on them. I have never had a hobby before because I can't concentrate. However in contrast to ADHD, I have good time management, able to relax easily, very good at planning and very very very organized. I often finish then when I start them, it just takes 10x as long because of my poor focus. I researched a mental state called "flow" and it appears to me that my brain does NOT have the ability to reach this state. I have never been engrossed in a task that I stay doing it for hours. Like I said, I've never had a hobby. I've never been hyper focused on anything. Another peculiar thing is that I'm a great listener. I have never "zoned out" before. Is this severe ADHD or something much more serious?