I Have What Appears To Be A Small Blister On

I have what appears to be a small blister on my left breast. It is not on the nipple. It goes from dry to oozing and has not improved in two weeks. Anytime I try to brush off the discharge, it will also bleed a little. I thought it might be a bug bite but it is just not healing. What should I do? It is about 3/4 of the diameter of a dime.