About a month ago I had unprotected sex with my girlfriend. It was in a car, so I didn't have any time after to clean myself up. After ejaculating I went to urinate, when I felt a painful burning as I was urinating. Ever since, I have have a burning sensation in the tip or my urethra. I do not have cloudy, smelling, or discolored urine, my penis does not have any bumps or discoloration, and it occasionally burns when I urinate, but not always. It is just this annoying burning pain in the tip of my urethra. When my boxers or pants catch it the wrong way it can cause very irritating pain. What could this be?