I also am young and deal with chronic debilitating fatigue. I've not heard that it is uncommon, but I've found quite a few members on our board deal with this. Unfortunately, my doctor have been unable to find a reason for my fatigue although going along with what Jen said, said I don't think my inflammation is well under control. I wish you luck in your journey to reduce your exhaustion.
ANA+, HLA-B27+, started Remicade June 2008, switched to Enbrel September 2010, switched to Humira April 2011, stopped biologics September 2011. Fusion already started, 25 years old.