Brief Answer:
Yeast most likely

Detailed Answer:
Hello and thank you for your question.
If it is itchy then yeast is most likey. It could also be some form of contact dermatitis or allergy if you have been exposed to something that you are sensitive to
From the photo you have included it does not look like herpes. Herpes usually presents with blisters, but in the early stages it could look similar to this rash. If it is burning and stinging and then turns into blisters I would be most concerned with herpes.
Gonorrhea and chlamydia usually present with burning in the penis expecially when urinating and they do not cause this type of rash usually.
However if you have had unprotected sex it would be good to get tested for sexually transmitted disease.
I suggest that if the rash is itchy you buy an over the counter antifungal cream and apply it to the rash twice a day. If it does not resolve see a doctor for evaluation and testing to determine the cause.
Regards,
Dr. Robinson

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