Anciendaze -- my daughter and I don't get fevers, either. Our normal body temperature runs low, about 96.8 F. I'm told that's not unusual with ME/CFS. After a really bad experience with my daughter and H1N1 last fall, I don't take her to the doc when she's sick because he says if her temp is 99 F she doesn't have a fever and therefore can't be sick.

Our latest workaround is to call in to the nurse, describe the symptoms say the her temp is 100 or 101F. 8 times out of 10 they don't want her to come in and either prescribe over the phone or say "wait it out".
I suspect, and I want to be clear it's just a suspicion, that in the early stages of ME/CFS our immune systems are
trying to fight infections, either XMRV or other infections we run into in everyday life, but because
something (XMRV?) is screwing up our immune function, that's not working well (low NK cell function?), so our bodies keep cranking up the immune system and we get muscle aches, fatigue, sensitivities, etc, which are immune reactions.
Maybe in the early days the symptoms come and go as our bodies manage to fight some infections down. During this stage we seem to not catch anything because our immune system is cranked up, but we also have symptoms of hyper-active immune systems.
Eventually our immune system either degrade too much (from XMRV?) or just flat wear out (immune exhaustion) and we start catching everything under the sun. We also might start seeing symptoms of latent infections reactivating or infections that people would ordinarily handle with no difficulty.
We still have
some immune function (unlike HIV-AIDS) patients, so maybe some infections come and go. Shingles is a lovely example of that. Perhaps our symptoms are changing depending on which infection is out of controll at any particular time.
I
suspect that most long-term more disabled patients have undetected/undetectable infections (mostly herpesvirus or maybe enterovirus, I'd guess) that have, over time, invaded cardiac and central nervous system tissue. They may be undetected because they've retreated to tissue and there isn't a lot in the blood, or perhaps the immune system is so exhausted it's not producing antibodies for the tests to detect.
By this thinking, any given treatment might help (temporarily) get rid of some infection that's giving you trouble, but because your immune system is a mess, you just get something else with different symptoms. Or you get the same thing back again before long. So it's a never-ending battle against an army of infections with an arsenal of different symptoms. :headache:
Just my current theory, subject to change as more info becomes available....