I think your doctor, even if inexperienced, is correct that this is not herpes. Lots of things come and go on the penis, such as irritation. Please leave the area alone, so the dermatologist will be able to tell what you have when you go. But this sounds like irritation to me, not an STD.
Please make sure the herpes test is available to the dermatologist. (I assume you mean a culture, not a biopsy.)
Take care.
Dr. Rockoff