It sounds like it could be fibro. But I wouldn't jump to that conclusion too fast. How long has the problem been going on? Myofascial pain syndrome can cause muscle fatigue and soreness as well, as can other things. I have both of those, and yeah, I do have periods where my muscles will contract involuntarily in localized areas of my body. I also have the "ran over by a truck" generalized soreness and pain.

Kell is right. It would probably be best for you to see a rheumatologist to get the problem checked out. I hope you find something, and start feeling better real soon!

Best Wishes...
Idealist