I'm 33 years old and this started about 3 yrs ago and has been getting progressively worse since. I'm not aware of any similar family history.
I'm not sure that this feel like fibromyalgia (although I'm not too familiar with it). This isn't pain so much as it is extreme fatigue. After I do strenuous activities, my muscles tend to tremble, get very weak and painful at that point. I've also been experiencing memory loss (not sure if this is related... but it started around the same time).
It could be fibromyalgia, I would ask your doctor for an epstein barr blood test and other tests to rule it out.
what's your age? how about your general health..family history of similar instances. these are important for an impartial view.