What Causes Swollen Pink Spots On Penis After Unprotected Sex?

Hi, I recently had a white dot on the shaft of my penis right above my scrotum. i figured it was a pimple so i tried to pop it but it wouldnt pop. Later i looked at it and it started to get pink and alittle swollen. That was four days ago. Today, i checked it out again to see how it was and it was getting better but still a decent size pink swollen smooth bump but i thought that i could see a very small white dot in the center so again i thought i could pop it but again it wouldnt pop and only got more swollen. And also it is painful.. i was just wondering as to what it might be? i don't think that it is an STd because there is only one and not a cluster of them. So what i would like to know is what is it? and what should i do about it? im 17 years old and have had unprotected sex with my current girlfriend ive had for 2 years now but she doesnt have any STD's or anything. So what could this be? and whatever it is how long will it take to go away?