Heat rash?

Anybody else got a heat rash on their belly? I woke up this morning and my stomach was red and warm and itchy. Then by dinner time it had turned to red dots whilst at work, I wear a few layers at work as I work in catering. And now my stomach is still itchy the red dots have faded a lot since this afternoon as I have my stomach out so the air is getting to it. Just wondering is it definitely a heat rash I have? It's nowhere els on my body . And if it is a heat rash why has it occurred? Thanks for any advice x