Most of my classes have lots of students in them and they tend to get very loud. I often cannot do class work because of my Sensory Overload. My teachers often don't understand when I go into Sensory Overload, and when it gets to a meltdown, they often yell at me and are unwilling to help. What can I do when this happens, and how can I get them to understand?
Have you asked your teachers for extensions on assignments, saying that since it's next to impossible to get the work done in the classroom you'd be better off doing it at home? Or asking if you can leave and come back when things have settled down a bit?
To be honest, I'd take the matter to the principle or something of that sort. I'm not one for certain people being placed into situations of ease, but if the class is causing learning problems and the teacher isn't able to do something about it, then they're at fault, and higher officials should say something to them about it.
Honestly, I would talk to the teacher about it in private. If things get bad then ask to go to the bathroom and clear your head for a minute or two before going back to class. And like Nashida said, asking your teachers for extra time on assignments might also be a good idea. Just tell them about your sensory overload and how all of the commotion in class keeps you from doing your work to the best of your ability.
Going directly to the teacher isn't very likely to solve your problem. Best thing you can do is go over your teachers' heads and talk to someone who can tell them how to best accommodate for your own situation. Talking to the principal(you're in high school I guess?) about this can get you somewhere at least. Usually teachers aren't the people to talk to about these kinds of things. It's not their fault, they just don't have that kind of power because then it could be unfair if they start to establish accommodations for you that are either too much or too little.
I hope this doesn't all end up with you getting an ADD label, at least not without good testing to prove. They toss that label around a lot these days and it isn't always deserving. I would talk to teachers about in private first. Sometimes a talk outside of the situation is all it takes. Failing that you basically have three options 1) Try and suck it up and treat it as white noise. 2) Bring it another staff that you trust (preferably higher rank but not neccessary. I've seen nurses and janitors pull some nice strings before) 3) Get creative. I once had this issue in study hall and would put in in-ear headphones but leave the music off. Harder to give straight forward advice on the last one because I don't know what you have to work with. You could just make it rediculous (like earplugs) to prove a point. Well these are work condition acomidations, not actual work accomidations. Teachers can attept to fix that but not all will.