White bumps on penis

Hello,

For some years now I have had 4 white bumps on the underside of my penis directly under the head. Because I am African-American these bumps are quite noticeable. 3 of the bumps are rather small but one is considerably larger in comparison to the others. I finally saw a doctor about this and he told me that I should just hold a warm towel over it and the heat would pop the bumps and they would go away. This did not happen and i am fairly convinced that there is no puss inside the bumps. The bumps appear to be more like abrasions than anything else. Can you tell me what these bumps are and how I can finally rid myself of them. I have attached a photo for your convenience. Thank you.