I believe that EBV is often the trigger for many of these illnesses. What research has shown is that in persons who have CFS, viral channels remain open as expressed by RNase L weights long after the viruses have effectively been eliminated. So basically... our body thinks it is still fighting an infection and that consumes our energy and ends up destroying our healthy cells.
There is considerable research that clearly dispells the myth that EBV causes CFS. However, it is true that some people that have EBV go on to suffer from chronic fatigue, but it is NOT directly attributed to the EBV infection. I myself am dealing with a very recent infection but had severe fatigue prior to EBV, that has gotten worse. Someone more familiar with CFS or fibro might be better able to answer the questions about tendonitis, muscle pain and twitches.