What Causes Swelling And Discoloration Of Finger?

I have been to a regular Doctor about my right index finger is swollen and purple at the tip back to the back of the finger nail. She gave me a 10 day supply of antibiotics. 10 days later, nothing, went back and they sent me to an othopedic Doctor, they put me on some super potent anitibiotic, 6 a day for 10 days, nothing, 2 xrays andall they came up with is "we are not sure why your finger is swollen and purple, no bone infection or infection what so ever" I am kind of fond of all my digits, do not know where to turn.