What rash is this on my baby?

Victoria • Mommy, wifey, foodie, wino, explorer, hair artist, traveler, dog lover, adventurer. 👶🏼👪🎬🌴🥂🍷🍻🌶🥩🌮🍕🍩💃🏼👙🌺☀️🌊

What the heck is this? It just popped up on Monday and I thought it was a heat rash at first... but I thought those go away in a day or so? What else can this be? Going to the doc later today but does anyone have any ideas???