Alison,
First, welcome to this community. It's too bad you have this terrible condition happening, but take whatever comfort you can from knowing you are not alone. There are a lot of caring people here.
I do not know the specific drug you mentioned, but you could very well be having some side effects. Trouble breathing? That is not something to fool around with. Have your mum insist they try something else. There are plenty to try. A lot of people respond very differently to every drug, especially powerful ones like what is used to fight RSD.
I am viewing and responding from work, so I can't take a lot of time with RSD information, but there is a ton of it out there. Look at the top of the main page for "useful links" and you will find many interesting articles.
Many have said that early detection is a big help in successful treatment. The fact that this is so new, and because of your young age, may work in your favor. I really hope so!
Glad to meet you.
Mike