It isn't an infection, its scar tissue. You shouldn’t have gotten it pierced with a ring...Mouth ulcer Treatment at home, Mix 1/4th of a teaspoon of sea salt with one cup of warm water. Dip a paper towel into it and hold it on your lip (on the bump) for 8 to 10 minutes. That will probably take care of it after a few weeks... But you should put a labret stud in it. It's hard to heal with a ring.
No matter what it will probably go away with time, but even if it doesn't you shouldn't worry about it. It's just a little bump and it's not like anyone is ever going to see it.
I'd need to see a picture to further determine what's wrong with your lip.