Drool, yeast or milk??

My baby has had this rash for about a wee or two now. it doesn’t bother her and her ped is out of town till the 15th. at first i thought it was just from her drooling anf spiiting up so much. but after reading some posts im thinking maybe a milk allergy? she is on formula. neither my son or i can drink cows milk but he never got a rash like this. She also spits up a good but after every single feeding.

*.yes i keep it as dry as possible and keepin either vaseline or a little powder on it.*