Exema ? red dots hives on skin in the heat high body temperature

Early this year,when i got in the heat i got hives and rashes like really bad,red splochs on my neck and red dots and hives all over me,i've also noticed that they come when im really angry,or in a hot shower,jacuazi,and anything to do with my body tempature getting hot,they itch really bad as well,and i noticed when i get out of the jacuzi with them and decide to get back in,i get like,pringlys everywhere.Its kinda annoying.Doctor didnt know what it was,i was told exema,or something but the stuff does NOT work.