Rashes On Arms, Inside Legs, Works On Extreme Climate. Are They Heat Rash?

Hello, I am 57 years old. I work as a inspector / consultant for a consulting firm. My job is very go, go go. working or traveling between 50 to 65 hours a week on average. little time at home and always trying to keep the clients happy. I work on large roofs and make sure that they are installed correctly, or according to our specificattions. The work is vey demanding and the weather right now is very warm / hot. Since last Friday I have noticed a type of rash on the inside of my arms, the back of my arms, and the inside of my legs by my growing? area. Do I have a heat rash perhaps? I have beenn doing this typeof work for almost 33 years and have never experianced this before. The rash is like a red area that varies from 1" to 1 1/4" across with a white spot in the middle. Some area's the smaller ones are maybe the size of an eraser on a #2 pencil. What do you think? Thanks