I definitely would consider ruling out lyme disease (and other possibilties, including MS) before you accept a fibro diagnosis.
Your symptoms could certainly be due to fibromyalgia, but I wanted to mention that a new national research institute in the U.S. that is researching CFS/ME, fibromyalgia, autism and other illnesses... is also researching what they refer to as 'atypical MS'.
Here is the link for that information if you are interested:
Also, if you get tested for lyme disease... please consider that often test results will be false negatives. There is a preferred lab here in the U.S. ( (http://www.igenex.com/), but I'm not sure about the U.K. In any event, consider getting tested more than once if your first result is negative. At least that way when you finally have your diagnosis, you will be more comfortable with it and also on the right treatment as well.