What Causes Burning Sensation And Black Bruise On Knee?

i had a slight burning sensation to the right side of my knee on only what i know was probly a vein in my left leg and it was tender and a bit itchy for awhile, it lasted about half an hour but then i noticed it started to bruise.. on the third day (to day) its about 3 inch circular almost black bruise, i can think that i knocked it... should i see a dr...