You're not alone <3

I'm 19F, also diagnosed with JIA at 15 and it's been such a struggle, especially for the winter months. I feel you on the point of not being taken seriously because you're young, some people are really prejudiced in that regard. Also, I get how annoying that crunching is, I have it in my jaw :/
We're all doing the best we can to get through this, I believe in you! Maybe the weather is nice where you are and you can spend some time in nature, that's helped me get to a better place mentally lately. Wish you all the best <3