Suggest Treatment For Bump Near Thumb Causing Soreness And Pain

I have a large pea size bump about 5 inches from the tip of my thumb, and the top part of my hand thumb area in sore. What is causing this pea size bump? It is right near my wrist thumb area. I just noticed it about a week ago. It seems to be growing. When I make circles with my left thumb, it hurts a bit where my thumb and wrist join.