What Causes Itchy Palm With Blue Bruises?

Yesterday, I felt itchy on my palm right under the middle finger. It looked swollen. Then I notice that there was a bruise. I don't think that I had any injury on my palm at that moment at least. I rinse my palm with cold water. After a few minutes, it was not swollen anymore but still looked a little blue (like a bruise). Today, the blue color turned light brown (almost gone), no pain. Is it possible something bite me causing all these? Or, is it possible I hurt myself accidentally without knowing it, then have all these problems after 10-40 minutes? This is the first time I have this problem.