You are right to be concered aboutl sexually acquire urethritis, such as gonorrhea, chlamydia, or non-chlamydial, nongonococcal urethrits (NGU). However, it is unusual for symptoms to appear once and then stop; if you had one of those, most likely you would have continued to notice abnormal penile discharge, underwear staining, and the like. However, it is possible you have one of those conditions and definitely should see a health care provider about it.