I Have Had Tenderness On The Inside Of My Right

I have had tenderness on the inside of my right forearm for a few days. No injury has occurred. This morning a bruise appeared from two inches below my wrist and running about four inches toward my elbow. In the last 6 hours or so the bruise has extended a couple of inches more. I take warfarin and my last INR was 2. its usually consistently around 2.5.