Did it just come on gradually? Do you feel like you've always got the flu?
I became very fatigued during my first pregnancy and never regained my previous energy level, but at that time it was just fatigue. (Eventually, they found I had Hashimoto's.) It was 7 years later, in 1982 after my third child was two, that I crashed.
There had been a couple of times, right before my crash, when I became very reactive after driving home with my car windows rolled down. Although I'd never had any sensitivities or allergies in the past, I would be exhausted and my whole body would ache for a couple of hours. Around that time (and it's hard to piece it all together in retrospect), my then husband got some sort of virus and became very ill for a couple of days and then got completely over it. For me it felt more like I kept getting a flu that never made me really sick, but that would go away and then come back, but never really leave.
Within a few months, I went from being an active mother, volunteer, and part-time student, to becoming mostly housebound (though not bedbound), unable to think, quite chemically sensitive, and all the rest of the classic CFS symptoms.
The first doctor that diagnosed me with CFS thought it had probably started back in 1975. Other than pregnancy, and a lot of personal stress at that time, I don't know of any other factors that could have triggered this illness. I did have a month long flu, in the spring of 1972, that was hitting many people very hard, but I recovered completely from that.
As I said, I have no idea where XMRV fits into my picture.