It is hard to say what the white pimple under the head of the penis is, without seeing it. It might be inflammation. What caused the inflammation might be more difficult to determine. The inflammation might be caused simply by increased friction (masturbation, rubbing). Sexual intercourse might be a cause for a sexually transmitted infection, which might have caused the inflammation. This is less likely because the inflammation caused by sexually transmitted diseases usually includes more than one pimple.


However, this sole fact cannot rule out the presence of sexually transmitted disease. Therefore, you are advised to visit your family doctor or a urologist for a physical examination, a urethral swab, and urine culture (the infection might have aready started spreading via the urine).