Unbelievable itching has been a part of my story, too, and I have wondered about some heat as a factor, but don't necessarily say that to a doctor, as you may be scoffed at, or ignored.
In a shower there may be agitation as well, and I have wondered about rubbing any affected area as parasites seem to use the activity for their own purposes...spreading the poison.
In fact, I have learned to consider a number of things as causal, then wait and see...taking no chances.
Most answers, when they come, are far more simple than I had ever dreamed.