What Causes Red Lump On The Wrist Bone?

all of a sudden a lump appeared on the back of my hand near my wrist. I had just bent my wrist down slightly and it felt very tight. Then red coloration started surrounding the lump (which does burn a bit). Now it has spread out, taking in my knuckles and fingers. Should I be concerned? Yesterday I got an INR test and it was 7.0. My Doctor said to stop my Warfarin for a couple days and gave me a new dosage plan starting on Monday.