Baby acne? Baby heat rash? Allergic reaction?

Mirian • Momma of 2 beautiful boys (9&4) currently pregnant w/ baby #3
My 1 month old has developed a bumpy rash on his face & I'm not sure what it is. I will be making a appointment first thing tomorrow morning but was wondering if anyone has had this happen to there little ones or if anyone knows what it is. He has a little on his head & chest but it's mostly on his face & ears.