Thats interesting. I assume you've been checked for a disorder called polymyositis? That's a disorder that has similar symptoms to FM but with high CPK levels according to the page below.
http://www.medicinenet.com/fibromyalgia/page3.htm
However according to the site below while your CPK levels are higher than normal, they are not nearly as high as in autoimmune conditions such as polymyositis, dermomyositis where CPK levels are in thousands. This suggests you're kind of in a limbo area where somethings going on but not at a severe level. Medicine is not really good at explaining this kind of abnormal but not disease causing test finding.
http://www.hopkins-arthritis.org/ask-the-expert/myositis-011/elevated-cpk-427.html