What Causes Increased Hair Fall After Washing Hair?

I am experiencing sudden hair loss, but ONLY when I wash it. I can brush it, and not much combs out, but during and after my shampooing, it starts shedding. This is new. I know that we all shed some everyday, but this is beyond normal. I am experiencing a bit of itching, but thought it was merely dry scalp because of indoor winter dryness of my overall skin. I have not changed any shampoos, etc, nor started or stopped any meds or supplements.