Small formation under skin of penis

I've always had a small rice size (about a fourth of an inch) formation about an inch below the head of the penis on the back side. It doesn't hurt unless a large amount of pressure is applied. It has not grown and it hasn't changed locations. I find it extremely bizarre and aggravating. It literally reminds me of a grain of rice stuck under the skin of the penis shaft. I've had it my whole life so I'm not sure if it affects me sexually but lately i've been having trouble achieving a full erection during sex. Any thoughts? Thank you.