I have a bump on my penis. It's on the shaft right under the head on the underside. I'm a virgin, so it's not an STD. The bump is slightly lighter than the rest of my penis and it doesn't itch, hurt or burn. It's also not a hair follicle or pimple because I know about those. I've had it a couple of months now and it's not getting any bigger or any smaller. Can somebody tell me what it is?