My younger brother started Accutane for about 2 months and has a bad rash, help please? (photos)

My brother has been taking accutane for about 2 months. His dermatologist recently upped the dosage so he can take it twice a day. He started having a really bad rash by his armpit. I took him to his pediatrician, she did a visual test and said it was herpes. Which didn't make sense to me because I was in wrestling and never saw herpes on the skin. I want a second opinion. I took accutane myself and know one of the side effects is a irritating rash.