What Causes Unusual Severe Pain In Right Index Finger?

Two days ago, I noticed severe pain in my right index finger. It was so severe that I could not pick up a cup. There is warmth to the touch and a bit of swelling. So far there does not seem to be a spreading of the pain. I saw my doctor who prescribed a steroid treatment. That was yesterday. This morning the pain was worse and the hand is more swollen. Can you advise?