Most probably its not chicken pox
. Chicken pox doesn't happen just like that. You need some one to have chicken pox to spread from them to him. Moreover chicken pox doesn't restrict itself in the bottom area. It could be allergy
or infection. Apply some calamine
lotion and if the problem persists or keeps worsening show it to a dermatologist/ pediatrciian for direct visual inspection and treatment accordingly.
Dr. Balaji Chinnasami MD
Assistant Professor - Pediatrics