Life is what you make it and procrastination may be holding you back, but you have to realize a few things before you can conquer it.
#1: Admit that you are the problem.
Because you are. For whatever reasons led up to this point, you caused them. It might hurt the ego, but given that you've already failed a few classes, you shouldn't have much of an ego anyway.
#2: Drop the "Smart but unmotivated" bullshit.
Because ultimately, it doesn't matter how smart you are if you can't bring yourself to do something. You could be Stephen Hawking, but without the motivation to stare endlessly at the stars and perform feats of physics while simultaneously being effected by a crippling chronic disease, you're the equivalent of those theoretical kids who get D's and F's because "They just don't get it."
Fun Fact: Public High school and Middle School work isn't meant to be hard. People that fail them are most often irresponsible rather than stupid, and it's still a reflection of yourself. Don't disassociate yourself from your grades by feeding the delusion that you're "smart and unmotivated."
#3: Acknowledge what is causing your problem, then deal with it.
Professional writers are notorious for having procrastination/distraction problems. They overcome it by acknowledging what is causing the problem, and then dealing with it. This often means doing things like disassociating themselves from their vices(gambling, drinking, gaming, internet, etc.)
Video games causing you a problem? Uninstall them from your computer. Thinking about not uninstalling them? Uninstall them anyway. Still not sure? Do it anyway. Fight it. Got a console? Unplug it. Put it in your closet, preferably in a box or multiple boxes. Make it harder for you to start a game than it is to start your work. Take the game discs and put them in a single case, and give them to someone you trust to keep them away from you.
Internet got you down? Disable your access in your computer. Can't do that? Uninstall your preferred browser or delete shortcuts to your browser from your desktop and menus. Block Reddit. Filter Imgur, Youtube, and Facebook, and social media. Make it harder to procrastinate.
No, this is not easy to do. Do it anyway, because you have something to prove.
#4 Swallow your pride.
Because you really don't have anything to be proud of right now. You're a C/D student who is easily distracted. Congratulations, you're 60% of lower to middle class males in that age range. Quit telling yourself your smart, or "you could do that if you really tried." No one cares about 'what ifs'. They care about what it is you've actually done, and whether or not you're fit to do it again, or do something more.
Someone with cognitive disabilities who simply tries is more impressive than someone who doesn't want to do the work. These days, people aren't limited by their intelligence or education as much as they are limited by their drive.