I Had A Bruise On My Arm About 3" Long

I had a bruise on my arm about 3" long and 2" wide. I hit it on a seat on an airplane. It turned dark purple and over the last two weeks has faded. First I noticed that when I touched it there is a pea-sized lump in the middle of it. Over the last several days it has developed white bumps only in the area of the bruise that are very itchy? What are they and what should I do for them?