25/yrs old. About four years ago i consumed 1-3 30g servings of soy
protein isolate per day as part of a weight training routine. I
stopped about two years ago as it was killing my appetite, and noticed
since that time my libido lowered dramaticaly. It was only a week ago
when i resumed consumtion of soy after many years that my libido shot
up again to what i would expect were normal levels. I would like to
maintain this level without having to consume the soy. what in the soy
protein is causing this as i have tried many proteins (whey egg)
e.t.c. and a plethora of supplements.

I've not heard specifically about soy increasing libido. I understand
soy has high concentrations of phytoestrogens, thought to reduce the
buildup of DHT in the scalp, and therefore reduce male pattern
baldness.

Wow.  A quick 5 minute search yeilded the opposite results, and comments like this:

..."Celibate monks living in monasteries and leading a vegetarian
lifestyle find soy foods quite helpful because they dampen libido..."

Another site said this (dampening the libido) was a myth, that there
are no studies that back this up...

There were many variations, but nothing there about increasing libido.
Maybe someone else can find studies to prove your premise...

As other have stated above, that is an unexpected reaction to a soy
product. There is some evidence that soy can reduce DHT
[DiHydroTestosterone]. But the male hormone system is complicated. I
think it might be possible that if this soy protein isolate was
reducing your DHT levels, it might cause changes or increases in the
other types of androgens (hormones) or possibly cause an increase in
the pre-cursers to DHT chemical in the blood stream.

Another explanation may be that your body was "rebounding" from DHT
depletion. In other words, as the soy was lowering your DHT, your body
made more to compensate, but actually made more than necessary.

Yet another thing you should consider is what else you were doing when
taking the soy protein isolate. Were you exercising more often? More
active? Any other supplements you were taking, like vitamins? The
lifestyle you were living at that time may have been different than
your lifestyle now, and these other factors can affect sex drive.

One final thing, "protein isolate" might have a different effect on
DHT than something like soy milk or other soy food products.