You need to see a doctor, as the previous answer advised. I once had a cat-scratch on the back of my hand which become infected. It took about five MDs, two skin specialists and a professor of Dermatology to eventually diagnose it as a 'Coral Staph' - a rare thing indeed.
About four lots of antibiotics didn't fix it. My own immune system must have cut in and, after about six months, it cleared of itself, leaving a white scar on the back of my hand I have to this day.
I doubt you have anything that serious, but get it checked out anyway.