Can be a lot of reasons. Can be because of season change, or can even be a Herpetic lesion.
I would advise one should post pictures in this case or take consultation.
Health Tips
Don't apply irrelevant creams over the lesions. Steroidal creams in case of infection will flare up the lesion, while antibiotic creams might or might not be needed. Entirely depends on the rash type and other symptoms like fever, cough, watering eyes, painful or not, itching present or not. Just a rash can mean many things. Do consult.