I Am 33 Years Old, About Three Years Ago I

I am 33 years old, about three years ago I noticed some brown spots around the base of my penis and a few on my scrotum. I use to shave regularly over the past few years they seem to have gotten a little more noticeable and there is a group of about 15 to 20. They are soft and brown and it raises a concern that I could have an STD or warts. However I did ask a RN on a Dr. visit and even showed him the spots. He said not to worry but don't shave as this could cause them to spread. Do I have moles, warts or an STD? I really want to identify the exact nature of these spots.