About 10 days ago I noticed a small pea sized lump about 2 below my left elbow on the side of my arm. At first, I thought this was a spider bite, but after 10 days, nothing has changed. The lump does not hurt, is not discolored, and can be moved around if I push it. I noticed that I press this part of my arm on my work chair while at the computer although I do not have a bump on my right arm or anywhere else. Also want to tell you that I play tennis twice a week using my left arm. Any idea what this could be?