I have had PR for over 10 years now. When I was first diagnosed, it said it could last anytime between 4 days and forever. I guess I am lucky to be the forever type (just kidding, of course). Add to that spinal stenosis and chiari1 malformation, and I am just one big mess. I have the same symptoms as you, which leads me to think you have the right diagnosis, I don't think age is a factor. We have just learned that my sister who has leukemia also has PR. Keep you chin up, and rest as much as you can, and don't ever feel guilty about it, you have to do what you have to do to feel reasonable good.
I did not mean to post so soon! I wanted to say that there are other conditions that are similar to PR that might fit a person of your age as well or better. Is your doctor a rheumatologist? If not, I think you need to see one as they are the most knowledgeable docs about autoimmune conditions.
I know how hard it can be to function with one of these conditions until you respond to the meds. Hang in there! You are among friends who understand what you are going through.
You are very young to have been given this diagnosis. While there are exceptions to every rule, I think that you should seek another opinion. Ask for your lab results, too, as they will provide additional information that can be helpful.