Rash??

So my son has this rash, the pediatrician initially said it was from all the drooling he does, but I can’t help to wonder if it could be from his formula. Awhile ago we were using parents choice formula with no problems but WIC doesn’t cover that so we switched to guerber soothe. Does this look like it could be an allergic reaction? I’ve tried Vaseline and A&D and nothing has worked which has led me to think it could be from the formula instead of drool.