If you happen to get a rash from prickly heat that comes with itchiness, try taking an antihistamine. This has happened to me. Taking an allergy pill really cut down on the itching I felt.
I have since taken to keeping antihistamines in my travel first aid kit in case I need a treatment for prickly heat rash symptoms. You might want to try to find a non-drowsy kind to be on the safe side.