Multiple bumps on scrotum skin

Hi, for quite some time i've been having this problem - there are white pimple-like bumps on my scrotum. It started out only on the left side but after 1.5 years or so it spread to the right side. Some of them I can pop and squeeze out a uniform white goo. Others seem to be deep under the skin and nothing helps. Some of them feel *solid* inside! I did a lot of research and I was led to believe it's sebaceous cysts, but the question remains how come they are spreading? I've been keeping myself clean and yet they don't go away. It's been like that for 3-4 years now and I am really worried, nothing helps, they don't go away (except some new small ones) and new pop up. They don't otherwise bother, hurt or itch. It is not STD because i haven't had any intercourse when they first started.