When doing sex education in school at around the same age you had sex, we got taught that white pimples on the penis could be a sympton of chlymidia, your best getting checked out asap
good luck x
Useually pimple like bumps are coused from herpes but you say they havent gone away have they gone away and come back or just never gone away becouse with herpes they goway and come back and so forth
Are the pimples close to each other or separately? do they have pus or not?. You might want to have it checked out. It might be nothing sexually transmitted or it might be HPV.