How to tell if these white pimples on my penis acne or herpes?

Pimples are acne: Herpes is distinctively painful; if you have acne elsewhere you'll know the difference. Herpes won't produce the unmistakable white / creamy pus from an acne lesion. Most teenaged guys get at least some acne on their shaft at some stage. Even though what you describe is probably not herpes, i hope you'll still choose to love safely and responsibly.

Sebaceous cysts: Herpes is a collection of blisters that as they age lose the top layer of the skin and have raw red ulcerated lesions. Herpes hurts. Acne on the penis is not normal and i doubt with sincere confidence that you have pimples on your penis. The more common benign situation is an oil or pus filled lesion known as a sebaceous cyst.