Hello guys, your topic is very interesting for me and as I have read them I decided to write p+one, because I had similar problem, called penis bump. I was scared because I was sexually active in that time, and few times I did not use a condom, but I was lucky and it was just a pimple neutralized by using some medical cream. According to your cases you should not be scared if you had sex with just one partner, and if your partner slept only with you in last few months. The best solution is going to dermatologist and than you can be relaxed.
A single bump on the shaft of the penis that is not sore, itchy, inflamed or filled with any fluid is unlikely to be related to an STD; I would recommend seeing a dermatologist, but an issue like this might be nothing more than an overactive follicle. It may get bigger during erections simply because there is more blood in the underlying tissue. You can help to keep the penis skin healthy by washing every day, making sure to clean under the foreskin if you are not circumcised, and to apply a penis vitamin cream (health professionals recommend Man1 Man Oil) to keep the skin moisturized, smooth and supple.