Suggest Treatment For Heat Rash

just got a heat rash saturday (after 4 hours of fishing in the direct sun 7-11am) on my left buttock. was very light maybe an 1/2" in dia area. sunday i had worked out in the heat for an hour (in the shade 7:30pm) replacing light bulbs in a freinds burnt head light. i noticed the next day it spread worse. i have 3 more areas but smaller in the area. the skin is dry like a hard callous? and looks more like it is bruised like the color of a fresh scar. i scratched the first one saturday night thinking it was a small pimple of some sort with an ingrown hair. i was wrong.