Does it feel like it's on the top of the skin, or under it? Herpes is on top of the skin, not under it, like a pimple.
A pimple is simply a clogged oil pore, and that can happen on your penis, too. It could also be an infected hair follicle. Does it seem like a hair is coming out of it?
Any doctor should be able to tell you if it's a pimple, and you don't have to bring up any sexual activity. It doesn't look like an STD. Are you able to access health care at all?
Did you have protected or unprotected sex? Oral, vaginal or anal sex?
It may be really tempting to pop it - don't do that. Even if it's just a pimple, popping it can cause an infection, scarring, etc. Don't put anything made for the face on your penis, either. Just use gentle soap and warm water on it.