Ok, probably just irritation- Bbuttons are notorious for it.
Could be caused by a change in jewelry, got bumped/rubbed on or simply overhandling it with 'less-than-sterile fingers'.
(I work at a shop)we always recommend to wash it twice daily with antibacterial soap, and if you can mix a solution of 1 cup hot (not scalding)water and 1/4teaspoon non-iodized seasalt (at most grocery stores, near regular salt, but must be NON-iodized) soak your piecing with the solution 5-10min twice a day until it goes away(if you can put it in a small glass/shotglass usually you can hold it against yourself without putting extra pressure on the piercing.) this draws out the irritation without causing trauma-don't pop it.
If you recently changed jewelry, the quality of the metal might not be as good. Try putting the previous back in. You should see results within a week.