Chicken pox or an Allergic reaction?

Anjanette • Mom of a handsome little boy 👶🏻
My son suddenly came up with a rash on just his legs this morning and still hasn't gone away, I've taken him a bath and applied calydryl for rash and I'm noticing it's starting to show
Up on his arm pit area, don't know if I should wait it out or take him to emergency.. has anyone had this problem?