Sometimes this problem happens when an area is repierced:

I got the bottom of my belly button pierced years ago. I let it close up three years ago. I got it re pierced two months ago. When the guy repierced it, he was able to put it through the first hole but it came out in a different spot then originally. In the middle of the barbell there was a small scar. A few days ago that scar rose above the skin and became a small red bubble in the middle of the barbell. I have been cleaning the piercing and the piercing itself seems to be in good condition. I dont know what caused this or how to get rid of it. It's not causing me pain but is not pretty to look at and I'm afraid it may be and infection of some sort.

Hi Erin,

Are you doing lots of saline soaks? That is one of the best things you can do in this situation to help with drainage.
See the instructions on this page: http://safepiercing.org/bodyAftercare.html
Some people get such a bubble to drain using hot compresses of clean moist towels. If a week of frequent saline soaks or compresses (3 times a day or more) does not help or if it gets worse, you may need to see a doctor.

From repiercing, sometimes an old channel becomes inflamed or infected after a new piercing is placed nearby. Due to continuous secretion or irritation from the previous piercing, occasionally these situations cannot be resolved satisfactorily and you will not be able to wear jewelry in the site.

Good luck and let me know how it goes.