pimple like bump on penis that won't go away

I noticed I had what looks like a pimple on the shaft of my penis. I also noticed a hair going through the center. There wasn't any puss or blood that came out and after a couple days it started to decrease in size and in 3 or 4 days was small enough that you could barely notice it unless you were looking for it.  It has been on my penis for about 2 weeks now. There is no puss or blood or anything coming out (except the growing hair).  It's just a small bump (like a little zit) that is a little red and it has hardened a little. Is this an infected hair follicle or something or some kind of STD?  It really isn't that noticeable, it just worries me that it hasn't gone away after 2 weeks.