Just remember: you're not in high school to learn chemistry or algebra or grammatical structure or whatever. Those are nice side effects. You're in high school to learn how to manage your time and effort. To learn how to plan ahead. Don't think of your homework as specific subjects. Think of them as a set of tasks that you just need to put onto the calendar. If you can turn 45 minutes of history homework into a nice little box on a planner, it's a whole lot less frustrating to actually knock it out when it's time comes.
3-5 hours of homework is a lot, but it's not the end of the world, especially because it sounds like you're really bad at planning out your time anyways, which usually means a lot of breaks. I'd bet that if you were actually motivated to get it done, you could do it in 3 hours max. Even better, you can knock it down into 4 45 minute sections, or 6 30 minute sections, or however much time each subject needs. I always found it way easier to sit down and do half an hour of math homework than to get started with 3 hours of all homework. It gives you an achievable goal. Don't take breaks before you've finished with a particular subject. All a break does is get you out of the zone.
To start with, write EVERYTHING down. Make a pretty planner with nice little boxes, or use your phone's calendar function. Whatever works for you. Just schedule everything on it. School, practices, shower, video games, bedtime, everything. As you internalize your routine you can maybe let some of the written stuff slide. Just stick to the schedule. It's tempting to come home and want to unwind for a minute and get on steam and maybe play a few games, but before you know it it's 10 PM and you haven't done a damn thing yet. Don't sign into steam until the alarm you have set for it goes off, and sign off of steam (all the way offline, not just away) when it's time to stop. That's really all you can do.
Also, fuck all this stuff about medication and ADD and stuff. This is something a LOT of high school kids go through. Like, 95% of kids. If you think medicine is something you need to function in everyday life, then go for it, but if you're looking for some adderall because you're struggling to sit down and do your homework after school, then I'd say forget it. The side effects aren't worth it.
Good luck, brother. Just remember that it gets so much worse a couple years from now when your schedule gets even less well-defined. Lock it down now and you won't have one of those cool panic meltdowns when you're halfway to winter break in your first year of college and you realize that you haven't done a damn thing besides eat weird dining hall food and get really really good at guitar hero.