What Causes Inflammation On The Penis?

hello, I havent had any sexual contact for 6 yrs now, im 28 and a little over a month ago I noticed the metus lips of my penis is raised on one side and is slightly red, it doesent hurt or burn when urinating but I do sometimes have feelings of not fully finished urinating. the day this symptom occured I moved my bowels at a public restroom and there was splash back while I flushed. Since then it's been like this, swollen and a bit uneven on one side. Is there anything I can do to treat the metus to make swelling go down? Thank you for your time and consideration.