help

Attention Deficit Disorder

Ok so where do i begin uhhh

I've been having a hard time keeping my focus on one thing at a time and I came to the conclusion that I had ADD. But I didn't want to believe it at first. I just thought maybe I didn't have enough willpower to stop procrastinating or I was just being lazy. I've looked up how to lessen ADD symptoms, I have a good diet, I do cardio often, I've taken a few supplements and these all helped a little bit but I'm still frustrated that I can't stay on task when it comes to mentally demanding work like school. Physical work is ok because I don't think a lot while doing it. It was never really a problem in early grade school until late high school and college since the material we learned in grade school was really easy. I can't really manage my attention span now and my grades are suffering because of it. It got worse when I quit smoking after new years and people would notice that sometimes I wasn't paying attention to them while talking and that I would change subjects really quickly. Yeah I'm just frustrated because nothing is working, the diet, the exercise, the supplements, the coping skills.