Hi. I'm 16, and I am sexually active. A day after I my partner and I had sex, I sat down on the toilet and realize that there was a small, red bump on the shaft of my penis. It was extremely small. It was in the mid-shaft area, and it was in the shape of a pimple, looked like a pimple, and popped like a pimple, but it had more of a sting to it. I'm just really curious if I could have an STI or STD, possibly HIV. It was just one, I haven't noticed any others.