Our German Shepard suffers greatly after a bath in anything but rainwater.  It's not the shampoo, it's the hard water for him.  Once I figured this out, I was able to experiment with water from the water softener, hose, and creek.  We noticed when he plays in the creek he is not itchy afterward.  So we bathe him with clean collected rainwater.  We had tried forms of pain meds etc. but the solution is rainwater baths and vigilant brushing.  We also found the omega skin coat effective.