I need help/advice

See, here's my situation: I'm a 16 year old boy, junior in high school, taking health science and medicine as an elective. And I'm failing so bad in 3-4 of my classes. But my biggest issue isn't the fact that I'm unorganized or way too sensitive to sound to pay attention in class; It's the fact I have the attention span of a plastic house plant. I can't focus enough to get anything done, and I always lie to my parents to get out of working so I can spend more time doing the things I actually enjoy. I know it's a problem, I know I'm screwing myself over because of this, I know that there's a problem that I need to solve. But I just can't bring myself to let go of wanting to be around my friends and do the things I love all the time. Old habits die hard and whatnot. I just really need help, advice, positive reinforcement, motivation, whatever. If anyone, especially others with ADHD/autism that have found solutions to their own problems, could give me a hand here, that would be incredibly appreciated. Thank you.