I’ve had misophonia since I was 12. My 18YO son has it too. Things we’ve done for him include putting a sound-making device (white noise) in his room (he hates the sound of people walking down the hall – he thinks everyone is stomping, even if we are tippy-toeing). We also bought him a pair of Here One ear buds – which allow the addition of sound, rather than just trying to mask all sound, which just makes your ears try that much harder to hear things. So far, these have been the best thing for him – he wears them during class, and just having the white noise allows him to hear the teacher, while ignoring the gum chewers, pen clickers, foot tappers, etc. They are pretty pricey ($300), but you can manage the same effect with your phone, some earbuds, and a white-noise app.
I do think the addition of sound is sometimes more helpful than trying to block out all sound.
I also agree with Karen above, that when you are in a good mood, it’s easier to cope.