What Is The Remedy For The Heat Rashes On Arms, Legs And Neck?

I'm 19, about 5 foot ten and about 165 lbs. I had been spending a lot of time in the sun recently. From Thursday to Sunday I was spending at least 12 hours in the sun a day, and it was over 90 degrees every day. I developed heat rash. I have been out of the sun for 3 days now, and the rash is still there. It's on my neck, legs, arms, and I believe my face. My arms are starting to swell up a bit too. Should I be concerned?