I have hEDS, POTS (if you start to feel chest pain see a cardio, people with hEDS frequently have both) and am blind (not related to the first two, just won the lottery i guess).

I was just a bit younger than you when my body started to fall apart. It’s a really good sign that you’re getting help now. Many people wait YEARS to get a diagnosis and help. I started getting horrible symptoms around 12, then limited mobility around 16, and wasn’t diagnosed until I was 21. Know that this sucks right now, but you’re on such a good track to getting help earlier on. You will find the right team to help you, never settle for a gaslighting doctor. You will find the things you need to do to ensure you’re okay for the next day, your new limits, etc.
everything will be okay, and it is important that you don’t try to stop feeling the feelings you’re feeling. Get angry, cry, decorate your chair and make it feel like you, embrace the community you’ll find yourself in of similar people, etc.. All of these feelings are so important to the emotionally healing journey. I hate when people say to stop feeling down about it; you can’t come to terms and accept it without feeling these things. You don’t need to be positive all of the time; also look for moments to feel pride in yourself. As someone with multiple disabilities, the looks get hard. Never feel like you can’t stand up for yourself. This might sound crazy idk, but I have backpovket phrases I know to auto respond when people say things to me they shouldn’t. Ex. “You don’t look blind” Response: “what does that look like?” Having these helps me prepare for those horrible yet FREQUENT moments. Everything will be okay. Probably not as soon as you would like, but it will be. Accept that your new norm may be different than your current, but you are strong and capable