Baby rash/pimples

My 1 and a half year old son has a rash that looks like pimples on his chin. It started maybe 5 days ago and figured it's because he's been drooling and licking his lips more. Within the past 2 days, he's had similar looking pimples show up on his butt. We did go and stay with my MIL. They use wood heat and it's a lot hotter than what we're used to and my son usually ends up with a small diaper rash from sweating in his diaper so much. But this time it looks so much different. I dont believe its yeast. I just dont know if the 2 rashes could be connected or have isolated causes.