I Have A Mole On My Side About Have Way

I have a mole on my side about have way down between my armpit and hipbone. Usually it is flat and bout 1/2 inch long. Now it is round like a bubble, filled with fluid and the brown skin part is raised half way up the bubble like its about to come off or shed. It is not painful. Is this just an infection or something more serious? What should I do?