I had this about 2 years ago, it was very painful. I went to my orthopedic hand specialist and she told me that it was the start of arthritis in my finger and that it would go away. She gave me a small splint like device and told me to wear it for a while because reducing movement in that joint would help it go away. She was right. about two weeks later the pain was gone and the bump is smaller.
It could be a wort. I had one on my ring finger for probably a year.