What kind of rash is this?

My son is 4 months old and going through a terrible drooling phase. I have to switch out bibs every 30 minutes at least and even then he somehow managed to soak through his clothes and get rashes. I’ve been cleaning his face and neck with Mustella cleansing water and it worked just fine until last week he seems to have gotten an allergic reaction to it. I know it was the Mustella water because it became red and irritated where I wiped:

I quickly wiped with water his face but forgot to wipe his neck as I was in a hurry to get to our mommy and me class. The redness on his face went away after 10 minutes and all seemed to be fine. But after having a 30 minute drive with him hysterical crying (bc he hates car rides and his car seat) I come home and notice his neck is super inflamed:

I spent the entire week being paranoid about putting anything not natural on it since idk what ingredient he had a reaction to so I’ve been cleaning with camomile tea to soothe, applying real aloe leaf extract (straight from our home plant) and using coconut oil if it seemed to get too itchy. It was healing great. Then today comes and I applied aquephor before today’s mommy and me class and knowing it was going to be another crazy cry session in the car and I get home to almost the same rash all over again!:

It seems to have spread and be bigger this time. So now I’m confused if this is drool rash,chemical burn, allergic reaction, heat rash, yeast infection. I feel so bad for him. I immediately gave him an oatmeal bath to help soothe it but again I’m terrified of applying anything to it as I have no idea what it is. Anyone have a similar experience? I’m considering not going to anymore mommy and me classes (although he really loves them) because of the car ride and knowing that may be helping to cause it. When I pick him up from the car seat he is soaked in sweat from screaming his head off for 20 minutes.