Need Medication For Heat Rashes On Forearms

I'm 26 and weigh 112 and no medical issues. for the last months I have been getting a heat rash on my forearms about every 2weeks, also normally I am cold when most are comfortable but lately I have been hot. To the point that every morning I am sweating and it can be 50 degrees outside and I will be comfortable in a t-shirt. Sometimes I am hotter then others. I have no idea what is going on.