Hi Sophie,
I am among the older of people here at 55. However, I started showing the first lupus signs when I was about 5. I wasn't diagnosed til I was 35, so there were a lot of years in there that I was not treated effectively. I think this is the cause of a bunch of long lasting issues from sle.
I do hope that you will be able to find the support you will need to battle this not so welcome companion. Take good care of yourself, work with your doctors...you are all members of a team. They can't help you without your being involved in the important decisions which will affect your life.
You are young, and you need to "be young", yet your body wants to do its own thing too. Compromise with your body is not an easy balance, but with time, you will get there. Try to not let yourself get down about the times your body wins. Keep your friends close and involved with your health so they understand that there are times you are not able to do everything you all want.
Enjoy life, savor the good times.
Sally